Formulations for 3D printing of hydrosilylation-modified polysilazanes

ABSTRACT

Some variations provide a preceramic resin precursor formulation comprising: first molecules comprising at least one Si—C bond and/or at least one Si—N bond, wherein the first molecules include at least one silyl hydride group (Si—H) available for hydrosilylation; and second molecules with at least one unsaturated carbon-carbon bond attached to a UV-active functional group. The first molecules and second molecules may be reacted, via hydrosilylation with a homogeneous or heterogeneous metal-containing catalyst, to produce third molecules comprising a hydrosilylation-modified polysilazane that contains the UV-active functional group. Many possible starting formulations are described, and methods are disclosed for carrying out the chemical reactions to generate the hydrosilylation-modified polysilazanes. The hydrosilylation-modified polysilazanes may then be 3D-printed and thermally treating to fabricate a ceramic material.

PRIORITY DATA

This patent application is a non-provisional application with priorityto U.S. Provisional Patent App. No. 62/554,623, filed Sep. 6, 2017,which is hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention generally relates to certain formulations suitablefor making preceramic polymers, which can be converted into ceramicstructures.

BACKGROUND OF THE INVENTION

In comparison with metals and polymers, ceramics are difficult toprocess, particularly into complex shapes. Because they cannot be castor machined easily, ceramics are typically consolidated from powders bysintering or deposited in thin films. Flaws, such as porosity andinhomogeneity introduced during processing, govern the strength becausethe flaws initiate cracks, and—in contrast to metals—brittle ceramicshave little ability to resist fracture. This processing challenge haslimited the ability to take advantage of ceramics' impressiveproperties, including high-temperature capability, environmentalresistance, and high strength.

Ceramic matrix composite (CMC) materials overcome many disadvantages ofconventional ceramics, such as brittle failure, low fracture toughness,and limited thermal shock resistance. Applications of ceramic matrixcomposites include those requiring reliability at high temperatures(beyond the capability of metals or polymers) and resistance tocorrosion and wear.

Recent advances in additive manufacturing have led to a multitude ofdifferent techniques, but additive manufacturing techniques developedfor ceramic materials only process unreinforced ceramics and not ceramicmatrix composites. Only a few of the commercially availablethree-dimensional (3D) printing systems offer printing of ceramics,either by selective curing of a photosensitive resin that containsceramic particles, selective deposition of a liquid binder agent ontoceramic particles (binder jetting), or selective fusion of a powder bedwith a laser. All these techniques are limited by slow fabricationrates, and in many cases, a time-consuming binder removal process. Bystarting with powders that need to be consolidated to a dense part, itis an almost insurmountable challenge to add reinforcement and createceramic matrix composites without fusing or reacting the matrix and thesecond phase, losing reinforcing capability. Furthermore, many additivemanufacturing processes introduce large thermal gradients that tend tocause cracks in ceramics. Pores, cracks, and inhomogeneities are oftenresponsible for the low strength and poor reliability of additivelymanufactured ceramic parts.

No mature method for 3D printing of ceramic matrix composites exists.Currently, CMC materials are limited to manual lay-up, molding, orthermoforming. There are also known techniques for sintering ceramicparticles or using ceramic particles printed in an organic binder, bothof which typically produce porous ceramics that have lower strength thanthe parent material. Ceramic structures are typically sintered ascompacted porous materials, severely limiting the manufacturablegeometries.

Formulations have been described for creating ceramic materials that canbe printed (additively manufactured) with various methods such asstereolithography techniques and laser sintering. These are typicallyunreinforced ceramics that do not contain a second phase and suffer fromlow fracture toughness. These methods are described in Zocca et al.,“Additive Manufacturing of Ceramics: Issues, Potentialities, andOpportunities” J. Am. Ceram. Soc., 98 [7] 1983-2001 (2015).

In addition, formulations which can create 1D or 2D ceramics, or verysmall 3D structures, have been described. See U.S. Pat. No. 4,816,497issued Mar. 28, 1989 to Lutz et al.; U.S. Pat. No. 5,698,485 issued Dec.16, 1997 to Bruck et al.; U.S. Pat. No. 6,573,020 issued Jun. 3, 2003 toHanemann et al.; U.S. Pat. No. 7,582,685 issued Sep. 1, 2009 to Arney etal.; and U.S. Patent App. Pub. No. US2006/0069176A1 published Mar. 30,2006 to Bowman et al.

Preceramic polymers are a class of polymers which allow, via a thermaltreatment, a conversion of a polymer part to a ceramic material.Typically, these preceramic polymers contain silicon (Si) in themolecular backbone, with the resulting material containing Si. There area wide variety of known preceramic polymers. Examples includepolysilazanes, borazine-modified hydridopolysilazanes, polysilanes,polycarbosilanes, silicone resins, polyborazines, polyvinylborazine,polyborazylene, and decaborane-based polymers. These preceramic polymershave been used to form specific polymer-based structures that can besubsequently heat-treated (pyrolyzed or sintered) to create nearnet-shape ceramic structures.

A stereolithography technique provides a method to build a 3D polymermicrostructure in a layer-by-layer process. This process usuallyinvolves a platform (e.g., substrate) that is lowered or raised into aphotomonomer bath in discrete steps. At each layer, a laser is used toscan over the area of the photomonomer that is to be cured (i.e.,polymerized) for that particular layer. Once the layer is cured, theplatform is lowered or raised by a specific amount, determined by theprocessing parameters and desired feature/surface resolution, and theprocess is repeated until the complete 3D structure is created. Oneexample of such a stereolithography technique is disclosed in U.S. Pat.No. 4,575,330 issued Mar. 11, 1986 to Hull et al.

Modifications to the above-described stereolithography technique havebeen developed to improve the polymer resolution by using laser opticsand special resin formulations. Also, modifications have been made todecrease the fabrication time of the 3D polymer structure by using adynamic pattern generator to cure an entire layer at once. One exampleof such a modification is disclosed in Bertsch et al.,“Microstereo-lithography: A Review” Materials Research Society SymposiumProceedings, Vol. 758, 2003. Another advancement to the standardstereolithography technique includes a two-photon polymerizationprocess, as disclosed in Sun et al., “Two-Photon Polymerization and 3DLithographic Microfabrication” Advances in Polymer Science, Vol. 170,169-273, 2004.

There exists a need for creating ceramic parts of various sizes through3D printing, for engineering and other applications, without relying oneither sintering of ceramic particles or the use of ceramic particlesprinted in an organic binder, both of which produce porous ceramics withreduced strength. Formulations are desired that allow for the directconversion of preceramic polymers to dense ceramics with properties thatapproach the theoretical maximum strength of the base materials.

There is commercial demand for additively manufactured (3D-printed)ceramics in many fields including industrial filtration (molten metalfilters, flow separators); metal processing (casting molds/blanks);implantable dental and medical devices; and semiconductor processing.Additive manufacturing of ceramic materials is also of interest forpropulsion components, thermal protection systems, porous burners,microelectromechanical systems, and electronic device packaging, forexample.

SUMMARY OF THE INVENTION

Some variations provide a preceramic radiation-curable resin compositioncomprising a molecule having the formula:

wherein:x=1 to 100 when repeat units are connected linearly or x=1 to 10 whenrepeat units are connected cyclically;y=0 to 100 when repeat units are connected linearly (or when there areno such repeat units present) or y=0 to 10 when repeat units areconnected cyclically;R₁ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group (including saturated or unsaturatedgroups), a halide, an ester group, an amine group, a hydroxyl group, acyano group, and combinations thereof;R₂ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group (including saturated or unsaturatedgroups), a halide, an ester group, an amine group, a hydroxyl group, acyano group, and combinations thereof;R₃ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group (including saturated or unsaturatedgroups), a halide, an ester group, an amine group, a hydroxyl group, acyano group, and combinations thereof;R₄ is a UV-active functional group that is capable of free-radicalpolymerization, cationic polymerization, or both of these; andthe carbon-carbon bond between R₄ and Si, depicted as

, is a single bond (C—C) or a double bond (C═C).

In some embodiments, R₄ is selected from the group consisting ofacrylate, methacrylate, vinyl ether, epoxide, cycloaliphatic epoxide,oxetane, thiol, alkyne, and combinations, analogues, or derivativesthereof that maintain UV activity. In certain embodiments when R₄ is athiol, the composition further contains an additional moleculecomprising two or more unsaturated C═X double bonds, two or more C≡Xtriple bonds, or at least one C═X double bond and at least one C≡Xtriple bond, wherein X is selected from C, S, O, N, or combinationsthereof.

When y>0, the x repeat units and they repeat units may be arranged in ablock copolymer, a segmented copolymer, a random copolymer, or analternating copolymer, for example. In some embodiments, the x repeatunits and they repeat units are arranged randomly. For example, if thehydrosilylation reaction occurs at random repeat units of the startingmolecule, the final polymer will be a random copolymer. If the repeatunits of the starting first molecule all contain Si—H groups (i.e.,R₃=H) and the hydrosilylation reaction completely converts all Si—Hgroups to the hydrosilylation reaction product, then y=0.

The composition further may comprise a photoinitiator that is effectiveto initiate polymerization at the UV-active functional group. Thephotoinitiator may be present in a concentration from about 0.001 wt %to about 10 wt % in the composition. The photoinitiator may be selectedfrom the group consisting of 2,2-dimethoxy-2-phenylacetophenone,2-hydroxy-2-methylpropiophenone, camphorquinone,bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, benzophenone, benzoylperoxide, and combinations thereof, for example.

In some embodiments, the photoinitiator generates free radicals from themolecule under exposure to light with a wavelength from about 200 nm toabout 500 nm for free-radical polymerization of the first molecule. Insome embodiments, the photoinitiator is a photoacid generator thatcleaves to form a Brønsted acid for cationic polymerization of the firstmolecule.

The composition further may comprise a radiation-trigger free-radicalinitiator active at a second wavelength that is substantially differentfrom a first wavelength for which the photoinitiator is active. In someembodiments, the composition further comprises a UV sensitizer that iscapable of reactive energy transfer to the photoinitiator.

The composition further may comprise a thermal free-radical initiatorselected from the group consisting of benzoyl peroxide, dicumylperoxide, 2,2′-azobisisobutyronitrile,platinum-carbonyl-cyclovinylmethylsiloxane complex,platinum-divinyltetramethyldisiloxane complex, and combinations thereof.

The composition further may comprise a free-radical inhibitor. Forexample, the free-radical inhibitor may be selected from the groupconsisting of hydroquinone, methylhydroquinone, ethylhydroquinone,methoxyhydroquinone, ethoxyhydroquinone, monomethylether hydroquinone,propylhydroquinone, propoxyhydroquinone, tert-butylhydroquinone,n-butylhydroquinone, N-nitroso-N-phenylhydroxylamine aluminum salt, andcombinations thereof. The free-radical inhibitor, when present, may beat a concentration from about 0.001 wt % to about 10 wt % in thecomposition.

The composition further may comprise a 3D-printing resolution agentselected from the group consisting of UV absorbers, fluorescentmolecules, optical brighteners, and combinations thereof. In someembodiments, the 3D-printing resolution agent is selected from the groupconsisting of 2-(2-hydroxyphenyl)-benzotriazole,2-hydroxyphenyl-benzophenones, 2-hydroxyphenyl-s-triazines,2,2′-(2,5-thiophenediyl)bis(5-tert-butylbenzoxazole),2,2′-(1,2-ethenediyl)bis(4,1-phenylene)bisbenzoxazole, and combinationsthereof. The 3D-printing resolution agent, when present, may be at aconcentration from about 0.001 wt % to about 10 wt % in the composition.

Optionally, the composition further comprises from about 0.1 vol % toabout 70 vol % of solid-phase fillers.

Other variations of the invention provide a preceramic resin precursorformulation comprising:

(a) a first material containing first molecules comprising at least oneSi—C bond, at least one Si—N bond, or at least one Si—C bond and atleast one Si—N bond, wherein at least one of the first moleculescomprise at least one repeat unit with a silyl hydride group (Si—H)available for hydrosilylation; and

(b) a second material containing second molecules with at least oneunsaturated carbon-carbon double bond attached to an R₄ group (R₄—C═C),and/or at least one carbon-carbon triple bond attached an R₄ group(R₄—C≡C), wherein R₄ is a UV-active functional group.

In some embodiments, the first molecules contain side groups selectedfrom the group consisting of hydrogen, halides, substituted orunsubstituted cyclic or acyclic alkyl groups, aryl groups, hydrocarbongroups containing C═X double bonds or C≡X triple bonds (X is C, S, O,and/or N), and combinations thereof. For example, the first moleculesmay contain side groups selected from the group consisting of vinyl,ethynyl, vinyl ether, vinyl ester, vinyl amides, vinyl triazine, vinylisocyanurate, acrylate, methacrylate, diene, triene, and combinationsthereof.

The first molecules further may contain one or more atoms selected fromthe group consisting of B, Al, Ti, Zn, Zr, O, N, P, S, Ge, andcombinations thereof.

In some embodiments, at least 10 wt % of the first molecules isinorganic. In some embodiments, at least 10 wt % of the first moleculesis Si.

The first molecules may be selected from the group consisting oftrivinylborazine; 2,4,6-trimethyl-2,4,6-trivinylcyclotrisilazane;1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasilazane;B,B′,B″-triethynyl-N,N′,N″-trimethylborazine;B,B′,B″-triethynylborazine; 1,2,3,4,5,6-hexamethylcyclotrisilazane;1,1,3,3,5,5-hexamethylcyclotrisilazane; 1,2-dimethylsilazane;1,1-perhydrosilazane; 1,3-divinyl-1,3-diphenyl-1,3-dimethyldisilazane;1,3-divinyl-1,1,3,3-tetramethyldisilazane;1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasilazane;1,1,3,3,5,5,7,7-octamethylcyclotetrasilazane;1,2,3,4,5,6,7,8-octamethylcyclotetrasilazane;1,1,3,3-tetramethyldisilazane; polymethylcarbosilane;polyallylcarbosilane; derivatives of any of the foregoing in which oneor more functional groups have been replaced with hydrido groups; andcombinations thereof.

In certain embodiments, the first molecules have the formula:

wherein:n=1 to 100 when repeat units are connected linearly or n=2 to 10 whenrepeat units are connected cyclically;R₁ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group, a halide, an ester group, an aminegroup, a hydroxyl group, a cyano group, and combinations thereof; andR₂ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group, a halide, an ester group, an aminegroup, a hydroxyl group, a cyano group, and combinations thereof; andR₃ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group, a halide, an ester group, an aminegroup, a hydroxyl group, a cyano group, and combinations thereof, withthe proviso that at least one R₃ group is hydrogen (i.e., at least oneof the repeat units contains a Si—H group).

In some embodiments, R₄ is selected from the group consisting ofacrylate, methacrylate, vinyl ether, epoxide, cycloaliphatic epoxide,oxetane, thiol, and combinations, analogues, or derivatives thereof thatmaintain UV activity.

The second molecules may be selected from the group consisting of allylmethacrylate, allyl acrylate, vinyl acrylate, vinyl methacrylate, allylmercaptan, 3,4-epoxy-1-butene, 4-vinyl-1-cyclohexene 1,2-epoxide,1,2-epoxy-5-hexene, 2-methyl-2-vinyl-oxetane, and combinations thereof.

The formulation further may comprise a homogeneous or heterogeneousmetal-containing catalyst. For example, a metal-containing catalyst maycontain a transition metal, e.g. Pt, Pd, Ru, Rh, Ni, Co, or acombination thereof. The metal-containing catalyst, when present, may beat a concentration from about 0.00001 wt % to about 5 wt % in theformulation.

In some embodiments, the transition metal is complexed with a ligandselected from the group consisting of halides, alkyl groups, arylgroups, aliphatically unsaturated groups, organosilicon groups, carbonmonoxide, and combinations thereof.

In some embodiments, the metal-containing catalyst is a heterogeneousmetal-containing catalyst, wherein the transition metal is disposed on asupport material selected from the group consisting of silica, alumina,silicates, aluminosilicates, zeolites, carbon, and combinations thereof.

In some embodiments, the metal-containing catalyst is a homogeneousmetal-containing catalyst, wherein the transition metal is dissolved orsuspended in a solvent selected from the group consisting of hexane,furan, tetrahydrofuran, 2-methyltetrahydrofuran, methylpyrrolidine, andcombinations thereof.

The metal-containing catalyst may be selected from the group consistingof chloroplatinic acid hydrate,platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex solution,tris(triphenylphosphine)rhodium(I) chloride,benzylidenebis(tricyclohexylphosphine)dichloro-ruthenium(II),dichloro(1,5-cyclooctadiene)platinum(II), platinum(II) acetylacetonate,and combinations thereof.

The formulation further may comprise an aprotic organic solvent in aconcentration from about 1 wt % to about 99 wt % in the formulation. Theaprotic organic solvent may be selected from the group consisting ofhexane, cyclohexane, toluene, diethyl ether, tetrahydrofuran,2-methyltetrahydrofuran, pyridine, n-methylpyrrolidine, chloroform, andcombinations thereof, for example.

The formulation further may comprise an inhibitor (e.g., apolymerization inhibitor) in a concentration from about 0.001 wt % toabout 10 wt % in the formulation. The inhibitor may be selected from thegroup consisting of hydroquinone, methylhydroquinone, ethylhydroquinone,methoxyhydroquinone, ethoxyhydroquinone, monomethylether hydroquinone,propylhydroquinone, propoxyhydroquinone, tert-butylhydroquinone,n-butylhydroquinone, 1,3-divinyltetramethyldisiloxane,1,3,5,7-tetravinyl-1,3,5,7-tetra-methylcyclotetrasiloxane,N-nitroso-N-phenylhydroxylamine aluminum salt, and combinations thereof.

Other variations of the invention provide a method of making apreceramic radiation-curable resin composition, the method comprising:

(a) obtaining a first material containing first molecules comprising atleast one Si—C bond, at least one Si—N bond, or at least one Si—C bondand at least one Si—N bond, wherein at least one of the first moleculesincludes at least one silyl hydride group (Si—H) available forhydrosilylation;

(b) obtaining a second material containing second molecules with atleast one unsaturated carbon-carbon double bond attached to an R₄ group(R₄—C═C), and/or at least one carbon-carbon triple bond attached an R₄group (R₄—C≡C), wherein R₄ is a UV-active functional group; and

(c) reacting, via hydrosilylation in the presence of a homogeneous orheterogeneous metal-containing catalyst, the first material with thesecond material, to generate a third material containing third moleculescomprising at least one Si—C bond, at least one Si—N bond, or at leastone Si—C bond and at least one Si—N bond, wherein the third moleculesfurther comprise a R₄—C—C—Si sequence and/or a R₄—C═C—Si sequence as ahydrosilylation reaction product.

In preferred embodiments, in step (c), the molar ratio of the secondmolecules to the first molecules is selected from about 1 to about n,wherein n is the average number of silyl hydride groups present in eachof the first molecules.

The metal-containing catalyst may comprise a transition metal selectedfrom the group consisting of Pt, Pd, Ru, Rh, Ni, Co, and combinationsthereof. The transition metal may be complexed with a ligand selectedfrom the group consisting of halides, alkyl groups, aryl groups,aliphatically unsaturated groups, organosilicon groups, carbon monoxide,and combinations thereof. In some methods, the metal-containing catalystis a heterogeneous metal-containing catalyst, wherein the transitionmetal is disposed on a support material selected from the groupconsisting of silica, alumina, silicates, aluminosilicates, zeolites,carbon, and combinations thereof. In other methods, the metal-containingcatalyst is a homogeneous metal-containing catalyst, wherein thetransition metal is dissolved or suspended in a solvent selected fromthe group consisting of hexane, furan, tetrahydrofuran,2-methyltetrahydrofuran, methylpyrrolidine, and combinations thereof.

The metal-containing catalyst may be selected from the group consistingof chloroplatinic acid hydrate,platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex solution,tris(triphenylphosphine)rhodium(I) chloride,benzylidenebis(tricyclohexylphosphine)dichloro-ruthenium(II),dichloro(1,5-cyclooctadiene)platinum(II), platinum(II) acetylacetonate,and combinations thereof.

Step (c) may be conducted in the presence of an aprotic organic solvent.Step (c) may be conducted in the presence of a polymerization inhibitor.

In some embodiments, step (c) is conducted in an inert atmosphere. Thereaction temperature for step (c) may vary, such as from about 10° C. toabout 125° C. The reaction time for step (c) may vary, such as fromabout 10 minutes to about 48 hours.

The method further may comprise purifying the third material, such aswith a technique selected from the group consisting of solvent/solventextraction, evaporation, distillation, vacuum distillation,chromatography, filtration, centrifugation, and combinations thereof.

The third material may be combined with a catalyst quencher to captureor poison the metal-containing catalyst. The weight ratio of thecatalyst quencher to the active metal in the metal-containing catalystmay be from about 0.001 to about 10, for example. In some embodiments,the catalyst quencher is selected from the group consisting of activatedcarbon, dimethyl maleate, dimethyl fumarate, benzothiazole,triphenylphosphine, and combinations thereof.

In certain methods, the first molecules have the formula:

and the third molecules have the formula:

wherein:m=1 to 100 and is the number of the second molecules that react witheach of the first molecules;n=1 to 100 when repeat units of the first molecules are connectedlinearly or n=2 to 10 when repeat units of the first molecules areconnected cyclically;n−m=0 or greater (e.g., 0.1, 0.5, 1, or greater);R₁ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group, a halide, an ester group, an aminegroup, a hydroxyl group, a cyano group, and combinations thereof;R₂ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group, a halide, an ester group, an aminegroup, a hydroxyl group, a cyano group, and combinations thereof;R₃ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group, a halide, an ester group, an aminegroup, a hydroxyl group, a cyano group, and combinations thereof;R₄ is a UV-active functional group, such as (but not limited to)acrylate, methacrylate, vinyl ether, epoxide, cycloaliphatic epoxide,oxetane, thiol, or combinations, analogues, or derivatives thereof; andthe carbon-carbon bond between R₄ and Si, depicted as

is a single bond (C—C) or a double bond (C═C).

The method further may include 3D printing and thermally treating thepreceramic radiation-curable resin composition to generate a ceramicmaterial.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The compositions, formulations, structures, systems, and methods of thepresent invention will be described in detail by reference to variousnon-limiting embodiments.

This description will enable one skilled in the art to make and use theinvention, and it describes several embodiments, adaptations,variations, alternatives, and uses of the invention. These and otherembodiments, features, and advantages of the present invention willbecome more apparent to those skilled in the art when taken withreference to the following detailed description of the invention inconjunction with the accompanying drawings.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly indicates otherwise. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as is commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs.

Unless otherwise indicated, all numbers expressing conditions,concentrations, dimensions, and so forth used in the specification andclaims are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending at least upona specific analytical technique.

The term “comprising,” which is synonymous with “including,”“containing,” or “characterized by” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps. “Comprising”is a term of art used in claim language which means that the named claimelements are essential, but other claim elements may be added and stillform a construct within the scope of the claim.

As used herein, the phrase “consisting of” excludes any element, step,or ingredient not specified in the claim. When the phrase “consists of”(or variations thereof) appears in a clause of the body of a claim,rather than immediately following the preamble, it limits only theelement set forth in that clause; other elements are not excluded fromthe claim as a whole. As used herein, the phrase “consisting essentiallyof” limits the scope of a claim to the specified elements or methodsteps, plus those that do not materially affect the basis and novelcharacteristic(s) of the claimed subject matter.

With respect to the terms “comprising,” “consisting of,” and “consistingessentially of,” where one of these three terms is used herein, thepresently disclosed and claimed subject matter may include the use ofeither of the other two terms, except when used in Markush groups. Thusin some embodiments not otherwise explicitly recited, any instance of“comprising” may be replaced by “consisting of” or, alternatively, by“consisting essentially of.”

This disclosure describes resin formulations, compositions, and methodsfor 3D printing of preceramic polymer parts that are then fired orpyrolyzed to produce a ceramic part. Ceramic materials are prepared froma starting preceramic monomer/oligomer formulation that can be used inUV-cure-based, direct, free-form 3D printing to form polymer compositeparts, which may then be directly converted to the ceramic material.Electromagnetic-radiation curability of the resin formulations enablesdefinition of three-dimensional shapes via 3D printing.

This disclosure also describes the production of 3D-printed ceramicparts. The 3D-printed ceramic material is prepared directly from3D-printed preceramic polymer material, which is prepared frompreceramic monomer formulations. The 3D printing may be done thoughstereolithography, UV (or other electromagnetic radiation) curing, laserrastering, digital light processing, liquid crystal device projection,or other techniques. Final ceramic materials include, but are notlimited to, silicon oxycarbo nitride (SiONC), silicon carbide (SiC),silicon nitride (Si₃N₄), silicon oxynitride (SiON), silicon carbonitride(SiCN), silicon boronitride (SiBN), silicon boron carbonitride (SiBCN),for example.

The invention in various embodiments applies to additively manufacturedcomponents, such as to reduce part count, scrap, or non-recurringengineering. Some embodiments apply to high-wear or high-temperatureapplications that would necessitate ceramic materials. Specificapplications of interest include, for example, propulsion structures(vanes, impellors, nacelles, and thrusters), control surfaces (fins andleading edges), hypersonic structures (thermal protection systems andheat shields), high-wear components (brakes, clutches, and rotors),catalyst support structures, pump components, filters, brakes, andclutches.

In particular, disclosed compositions include a hydrosilylation-modifiedpolysilazane which adds UV functionality to the polysilazane precursor.The UV functionality may include, but is not limited to, acrylate,methacrylate, epoxide, or thiol functionalities. Polysilazane precursorsmay include linear or cyclic molecules and may have a secondaryfunctionality, such as a vinyl group for thermal crosslinking, orcomplimentary UV functionality, such as unsaturated bonds for thiol-enecrosslinking. As disclosed in detailed herein, vinyl or allyl additionto the polysilazane, via hydrosilylation, adds a side group to thepolysilazane chain. A vinyl or allyl group is bonded to a UV-activefunctional group.

As used herein, “hydrosilylation” means the addition of Si—H bondsacross unsaturated bonds, such as unsaturated carbon-carbon bonds. Thehydrosilylation reaction may be catalyzed or uncatalyzed. Typically, thehydrosilylation reaction is conducted catalytically and the substratesare unsaturated organic compounds. Alkenes and alkynes give alkylsilanes and vinyl silanes, respectively; aldehydes and ketones givesilyl ethers.

“Preceramic” in this disclosure refers to the capability to beultimately converted to a ceramic material. A “preceramic composition”is a composition that can be converted into a ceramic material, eitherdirectly (e.g., by pyrolysis) or via multiple steps (e.g., bypolymerization followed by pyrolysis). In particular, a preceramiccomposition may contain a preceramic polymer that can be pyrolyzed intoa ceramic material, a resin that can be polymerized into a preceramicpolymer, or both of these.

A “preceramic polymer” is characterized in that at least some of thepolymer converts to a ceramic material when heated to a temperatureabove 200° C. at atmospheric pressure in a substantially inert gasenvironment. Preferably, at least 50 wt %, more preferably at least 90wt %, and most preferably at least 99 wt % (e.g., essentially all) ofthe polymer converts to a ceramic material when heated to a temperatureabove 200° C. at atmospheric pressure in a substantially inert gasenvironment.

As intended herein, a “resin” means a composition capable of beingpolymerized or cured, further polymerized or cured, or crosslinked.Resins may include monomers, oligomers, prepolymers, or mixturesthereof. As used herein, “polymer resin” means monomer, oligomer,prepolymer, or other molecule that is converted to a polymer.

“Radiation-curable” in this disclosure is synonymous with“electromagnetic radiation-curable.” All references to “UV,”“UV-curable,” “UV-cure-based” and the like shall include reference notonly to ultraviolet radiation but also other electromagnetic radiationbands that can be effective in various embodiments, including microwaveradiation, terahertz radiation, infrared radiation, visible radiation(light), ultraviolet radiation, and X-rays. The radiation-curable liquidcomposition may be a UV-curable inorganic or organic composition, forexample.

As used herein, a “UV-active functional group” is a chemical group inthe form of multiple atoms bonded together in a functional group thathas absorption in the UV or visible region of electromagnetic radiation(wavelengths from about 100 nm to about 700 nm). Absorption (UVactivity) occurs when a UV-active molecule absorbs ultraviolet orvisible light that excites valence electrons, causing an electronictransition from a ground state to an excited state. UV absorption can bemeasured by a UV-visible spectrophotometer, which provides a spectrum ofabsorption versus wavelength.

In some variations, a preceramic resin precursor formulation comprises:

-   -   (a) a first material containing first molecules comprising at        least one Si—C bond, at least one Si—N bond, or at least one        Si—C bond and at least one Si—N bond, wherein at least one of        the first molecules comprises a repeat unit with a silyl hydride        group (Si—H) available for hydrosilylation; and    -   (b) a second material containing second molecules with at least        one unsaturated carbon-carbon double bond attached to an R₄        group (R₄—C═C), and/or at least one carbon-carbon triple bond        attached an R₄ group (R₄—C≡C), wherein R₄ is a UV-active        functional group.

The Si—N and/or Si—C bonds are contained in backbone repeat units of asilazane (monomer), a polysilazane (oligomer or polymer), a carbosilane(monomer), and/or a polycarbosilane (oligomer or polymer). When thefirst molecules contain at least one Si—N bond, with or without Si—Cbonds also present, the first molecules are referred to herein assilazanes (when monomers) or polysilazanes (when oligomers or polymers).When the first molecules contain Si—C bonds but no Si—N bonds, they arereferred to herein as carbosilanes (when monomers) or polycarbosilanes(when oligomers or polymers).

The first molecule must contain at least one Si—H (silylhydride) group,available for hydrosilylation. When the first molecule is a polymer withn repeat units, at least one of the repeat units must contain a Si—Hgroup, but the other repeat units do not need to contain a Si—H group.Multiple Si—H groups may be present in the same repeat units, in someembodiments. When there are n repeat units within a polymeric firstmolecule (n>1), the number of Si—H groups may be as low as 1 (a singleSi—H group within the entire polymer) and as high as 2n when allfunctional groups bonded with Si in the first molecule are hydrogen. Inthis disclosure, the R₃ group that is bonded to Si is hydrogen, for atleast one repeat unit. Of the overall molecule, the percentage of R₃groups that is H may be 100%, about 90%, about 80%, about 70%, about60%, about 50%, about 40%, about 30%, about 20%, about 10%, or about 5%,for example.

Also, the first molecule may be a copolymer that contains a silazaneand/or a carbosilane as well as another type of polymer. In these cases,the portion of copolymer that is a silazane and/or a carbosilanecontains at least one repeat unit containing a Si—H group, and maycontain a higher concentration of Si—H groups as described above forhomopolymers of silazanes and/or a carbosilanes. The other type ofpolymer may itself be a silazane and/or a carbosilane, but one that doesnot necessarily contain a Si—H group.

In addition to the R₃ groups, the first molecules may contain sidegroups or chains, R₁ bonded to the Si atoms and R₂ bonded to the N or Catoms of the silazane or carbosilane molecules, respectively. R₁ and R₂may be selected from, but are not limited to, hydrogen or organic orinorganic side chains or functional groups, e.g. halides, substituted orunsubstituted C₁-C₁₈ groups, cyclic or acyclic alkyl groups, arylgroups, hydrocarbon groups containing unsaturated C═X double bonds orC≡X triple bonds (X is C, S, O, and/or N). Exemplary functional groupsinclude vinyl, ethynyl, vinyl ether, vinyl ester, vinyl amides, vinyltriazine, vinyl isocyanurate, acrylate, methacrylate, diene, triene, ora combination thereof.

Substitution on any unsaturated bonds of the first molecules may includeany atoms, such as H, F, Cl, Br, or functional groups such as alkylgroups, esters, amine groups, hydroxyl groups, or cyano groups. Thefirst molecules may contain combinations of different unsaturated bonds.Common unsaturated bonds are C═C double bonds at the terminal positionof the molecules. For example, three substitutions on the C═C bonds maybe hydrogen atoms.

The first molecules may also contain additional atoms in the main chain(i.e., as R₁ or R₂ themselves) or in side chains (i.e., chemicallycontained within R₁ or R₂). Examples of other atoms include, but are notlimited to, B, Al, Ti, Zn, Zr, O, N, P, S, and/or Ge. The non-carbonatoms may be a part of cyclic or acyclic groups or structures.

Exemplary first molecules include, but are not limited to,trivinylborazine; 2,4,6-trimethyl-2,4,6-trivinylcyclotrisilazane;1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasilazane;B,B′,B″-triethynyl-N,N′,N″-trimethylborazine;B,B′,B″-triethynylborazine; 1,2,3,4,5,6-hexamethylcyclotrisilazane;1,1,3,3,5,5-hexamethylcyclotrisilazane; 1,2-dimethylsilazane;1,1-perhydrosilazane; 1,3-divinyl-1,3-diphenyl-1,3-dimethyldisilazane;1,3-divinyl-1,1,3,3-tetramethyldisilazane;1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasilazane;1,1,3,3,5,5,7,7-octamethylcyclotetrasilazane;1,2,3,4,5,6,7,8-octamethylcyclotetrasilazane;1,1,3,3-tetramethyldisilazane; polymethylcarbosilane;polyallylcarbosilane; derivatives of any of the foregoing in which oneor more functional groups have been replaced with hydrido groups; andcombinations thereof.

The first molecules are present at a concentration from about 1 wt % toabout 99 wt % of the preceramic resin precursor formulation. In variousembodiments, the first molecules are present at a concentration of about2, 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 95, or 98 wt %,including all intervening ranges.

The second molecules contain a UV-active functional group, R₄. TheUV-active functional group may be selected from, but not limited to,acrylate, methacrylate, vinyl ether, epoxy, oxetane, thiol, alkyne, or acombination thereof. Exemplary second molecules include allylmethacrylate, allyl acrylate, vinyl acrylate, vinyl methacrylate, allylmercaptan, 3,4-epoxy-1-butene, 4-vinyl-1-cyclohexene, 1,2-epoxide,1,2-epoxy-5-hexene, 2-methyl-2-vinyl-oxetane, or a combination thereof.

The second molecules are present at a concentration from about 1 wt % toabout 99 wt % of the preceramic resin precursor formulation. In variousembodiments, the second molecules are present at a concentration ofabout 2, 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 95, or 98 wt %,including all intervening ranges.

The sum of first molecules and second molecules may form a concentrationfrom about 2 wt % to about 99.9 wt % of the preceramic resin precursorformulation. In various embodiments, the first and second molecules,taken together, are present at a concentration of about 5, 10, 15, 20,25, 30, 40, 50, 60, 70, 80, 90, 95, or 99 wt %, including allintervening ranges.

The weight ratio of the second molecules to the first molecules may varyfrom about 0.1 to about 32, such as about 0.5, 1, 2, 3, 5, 10, 15, 20,25, or 30. In some embodiments, the weight ratio of second molecules tofirst molecules is dependent on the ratio of thiol to vinyl. Forexample, in certain embodiments there is at least one thiol functionalgroup per vinyl group.

In preferred formulations, the molar ratio of the second molecules tothe first molecules is selected from about 1 to about n, wherein n isthe average number of silyl hydride groups present in the firstmolecules, i.e., the number of individual Si—H bonds within the entirepolymer chain. When the molar ratio of the second molecules to the firstmolecules is equal to 1, there is an average of only one second moleculefor each first molecule. When the molar ratio of the second molecules tothe first molecules is equal to n, there is an average of one secondmolecule for each repeat unit of the polymer chain of the firstmolecule. As an example, when n=100 and the molar ratio of the secondmolecules to the first molecules is equal to n, then 100 secondmolecules react with each first molecule. In this case, if each repeatunit of the first molecule contains one Si—H group, then one secondmolecule reacts with each repeat unit of the first molecule.

In certain embodiments, there is an excess of second molecules in thereaction pot, so that a mixture may be provided in which the molar ratioof the second molecules to the first molecules is larger than n, such as2n, 3n, or more. In other certain (less-preferred) embodiments, there isless than one hydrosilylation reaction of second molecules per firstmolecule, in which case the molar ratio of the second molecules to thefirst molecules is less than 1, such as 0.5, 0.1, or less.

As stated above, hydrosilylation is typically catalyzed. Therefore, inpreferred embodiments, a metal-containing catalyst is present in thepreceramic resin precursor formulation, or added at a later time tocarry out the desired reaction.

The metal-containing catalyst may be a homogeneous catalyst, wherein thecatalyst is soluble or suspended in a liquid solution of reactants. Themetal-containing catalyst may be dissolved or suspended in a solvent,such as hexane, cyclohexane, toluene, furan, tetrahydrofuran,methyltetrahydrofuran, methylpyrrolidine, pyridine, chloroform, or acombination thereof.

The metal-containing catalyst may be a heterogeneous catalyst, whereinthe catalyst is in a different phase than the reactants. Typically, aheterogeneous catalyst is in a solid phase and reactants are in a liquidor vapor phase. Heterogeneous catalysts may be supported on a catalystsupport, such as silica, alumina, silicates, aluminosilicates, zeolites,or carbon, for example. Mesoporous silica in the form of MCM-41 orSBA-15 may be used, in certain embodiments.

Metal-containing catalysts (whether homogeneous or heterogeneous) mayinclude metal complexes of the form M-L, wherein M is selected from thetransition metals (e.g., Pt, Pd, Ru, Rh, Ni, and/or Co), and wherein Lis a ligand selected from halides, alkyl groups, aryl groups,aliphatically unsaturated groups, organosilicon groups, carbon monoxide,or a combination thereof.

Exemplary metal-containing catalysts include, but are not limited to,chloroplatinic acid hydrate (Speier's catalyst),platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex solution(Karstedt's catalyst),benzylidenebis(tricyclohexylphosphine)dichloro-ruthenium(II),tris(triphenylphosphine)rhodium(I) chloride,dichloro(1,5-cyclooctadiene)platinum(II), platinum(II) acetylacetonate,platinum supported on silica, platinum supported on alumina, platinumsupported on activated carbon, Pt/MCM-41, Pt/SBA-15, or a combinationthereof.

The metal-containing catalyst may be present from about 0.00001% (0.1ppm) to about 5% by weight of the reaction mixture (the preceramic resinprecursor formulation). In some embodiments, the preceramic resinprecursor formulation contains no catalyst, such as when uncatalyzedhydrosilylation is utilized or when the catalyst will be added to thereaction mixture at a later time.

A solvent may be employed to dissolve or suspend the first and secondmolecules to be reacted. For example, an aprotic organic solvent may beutilized, such as (but not limited to) hexane, cyclohexane, toluene,diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, pyridine,n-methylpyrrolidine, chloroform, or a combination thereof. The solventmay be in a concentration from 0 wt % to about 99 wt % of the preceramicresin precursor formulation. In various embodiments, the solvent ispresent in a concentration of about 10, 20, 30, 40, 50, 60, 70, 80, or90 wt % of the formulation.

An inhibitor may be added in a sufficient amount to inhibit prematurepolymerization and/or to stabilize the formulation. Inhibitors may befree-radical inhibitors, cationic polymerization inhibitors,hydrolsilylation inhibitors, or another type of inhibitor. Inhibitorsmay include, but are not limited to, hydroquinones such astert-butylhydroquinone, methylhydroquinone, ethylhydroquinone,methoxyhydroquinone, ethoxyhydroquinone, monomethylether hydroquinone,propylhydroquinone, propoxyhydroquinone, and n-butylhydroquinone.Inhibitors may alternatively, or additionally, include1,3-divinyltetramethyldisiloxane,1,3,5,7-tetravinyl-1,3,5,7-tetra-methylcyclotetrasiloxane, or acombination thereof. The inhibitor(s) may be in a concentration from 0wt % to about 5 wt % of the preceramic resin precursor formulation, forexample. In various embodiments, the inhibitor is present in aconcentration of about 0.1, 0.5, 1, 2, 3, 4, or 5 wt % of theformulation.

In some embodiments of the invention, the second molecules are insertedinto the backbone of the first molecules to create third molecules, viahydrosilylation:

wherein:n=1 to 100 when repeat units of the first molecules are connectedlinearly or n=2 to 10 when repeat units of the first molecules areconnected cyclically;m=1 to 100 and is the number of second molecules that react with each ofthe first molecules (m cannot be greater than n);R₁ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group (including saturated or unsaturatedgroups), a halide, an ester group, an amine group, a hydroxyl group, acyano group, and combinations thereof; andR₂ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group (including saturated or unsaturatedgroups), a halide, an ester group, an amine group, a hydroxyl group, acyano group, and combinations thereof; andR₃ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group (including saturated or unsaturatedgroups), a halide, an ester group, an amine group, a hydroxyl group, acyano group, and combinations thereof, with the proviso that at leastone R₃ group is hydrogen (i.e., at least one of the repeat unitscontains a Si—H group); andR₄ is a UV-active functional group.

When R₃=H for all repeat units and when m=n, i.e. there isstoichiometric conversion of reactants, n−m=0 and the second repeatunits are not present in the product.

The unsaturated carbon-carbon bond in the second reactant (secondmolecules), depicted as

, is a double bond (C═C) or a triple bond (CC). The carbon-carbon bondbetween R₄ and Si in the product (third molecules), depicted as

, is a single bond (C—C) or a double bond (C═C). In particular, thecarbon-carbon bond between R₄ and Si in the product is a single bondwhen the second molecules contain a double bond (vinyl group), and is adouble bond when the second molecules contain a triple bond (alkynegroup). Note that these carbon-carbon bonds may include hydrogen atoms(not explicitly shown) or other atoms in place of hydrogen, such ashalogens.

The third molecules are hydrosilylation-modified silazane or carbosilanematerials that include UV-active functionality via the added R₄ group.

Some variations therefore provide a preceramic radiation-curable resincomposition comprising a molecule having the formula:

wherein:x=1 to 100 when repeat units of the first molecules are connectedlinearly or x=1 to 10 when repeat units of the first molecules areconnected cyclically;y=0 to 100 when repeat units of the first molecules are connectedlinearly or y=0 to 10 when repeat units of the first molecules areconnected cyclically;R₁ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group (potentially including substitutionswith R₄ in place of a hydrogen atom), a halide, an ester group, an aminegroup, a hydroxyl group, a cyano group, and combinations thereof;R₂ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group, a halide, an ester group, an aminegroup, a hydroxyl group, a cyano group, and combinations thereof;R₃ is selected from the group consisting of hydrogen, a C₁-C₁₈unsubstituted or substituted group, a halide, an ester group, an aminegroup, a hydroxyl group, a cyano group, and combinations thereof;R₄ is selected from the group consisting of a UV-active functional groupthat is capable of free-radical polymerization, cationic polymerization,or both of these; andthe carbon-carbon bond between R₄ and Si, depicted as

is a single bond (C—C) or a double bond (C═C).

When y>0, the x repeat units and they repeat units may be arranged in ablock copolymer, a segmented copolymer, a random copolymer, or analternating copolymer, for example. In some embodiments, the x repeatunits and they repeat units are arranged randomly. For example, if thehydrosilylation reaction occurs at random repeat units of the startingmolecule, the final polymer will be a random copolymer.

If the hydrosilylation reaction completely converts all Si—H groups tothe hydrosilylation reaction product, and all repeat units of the firstmolecules contained Si—H groups, then y=0. If the hydrosilylationreaction completely converts all available Si—H groups to thehydrosilylation reaction product, but less than all of the repeat unitsof the first molecules contained Si—H groups, then y>0 even with aperfectly stoichiometric hydrosilylation reaction.

In certain embodiments, both R₁ and R₃ are hydrogen in the firstmolecules (e.g., perhydropolysilazane). The hydrosilylation reactiontherefore occurs at both of these sites, resulting in two —C—C—R₄ or—C═C—R₄ groups in each repeat unit. In these cases, the R₁ group can beconsidered a C₂ substituted (saturated or unsaturated) group in which R₄is substituted into R₁.

In some embodiments, the preceramic radiation-curable resin compositioncomprises a thiol-containing monomer, oligomer, or polymer, and anadditional molecule (an ene component) for UV-activated reaction.Possible ene components may include olefinic, acetylenic, allenic,aromatic, cyclopropyl, and carbon-hetero bonds. The additional moleculemay include unsaturated C═X double bonds or C≡X triple bonds, wherein Xis C, S, O, and/or N. Substitution on the unsaturated bonds may includeany atoms such as H, F, or Cl, or groups such as alkyl groups, esters,amine groups, hydroxyl groups, or cyano groups.

The preceramic radiation-curable resin composition may contain variousadditional components to assist in the UV-curing chemical reactions, orfor other reasons. The additional components may be added after theresin composition is formed. Alternatively, or additionally, theadditional components may be introduced to the starting resin precursorformulation (the first and second molecules).

In some embodiments, the radiation-curable resin composition comprises aphotoinitiator that generates free radicals under light exposure. Invarious embodiments, light exposure is produced from light having one ormore wavelengths selected from about 200 nm to about 700 nm, such asabout 250, 300, 350, 400, or 500 nm. The photoinitiator may generatefree radicals under light exposure by intramolecular bond cleavage orintermolecular hydrogen abstraction, for example. Photoinitiators may beused when the polymerization is, or includes, free-radicalpolymerization.

For example, the photoinitiator may be selected from the groupconsisting of 2,2-dimethoxy-2-phenylacetophenone,2-hydroxy-2-methylpropiophenone, camphorquinone,bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, benzophenone, benzoylperoxide, thioxanones, thioxanthones, and combinations thereof. Oxygenand nitrogen dioxide may also be used as a photoinitiator. Thephotoinitiator, when included, may be present in a concentration fromabout 0.001 wt % to about 10 wt % in the composition. In variousembodiments, the photoinitiator is about 0.001, 0.005, 0.01, 0.05, 0.1,0.5, 1, 2, or 5 wt % of the composition.

A combination of different types of photoinitiators may be used in thepolymerization process. More than one photoinitiator may be included toallow multi-wavelength curing.

When a photoinitiator is present, the composition may further comprise aradiation-trigger free-radical initiator active at a second wavelengththat is substantially different from a first wavelength for which thephotoinitiator is active.

The composition may further comprise a thermal free-radical initiatorthat generates free radicals under elevated temperature conditions. Theaddition of thermal initiator allows for multiple-mechanism curing inthe formulation—i.e., both UV and thermal curing. In some embodiments, athermal free-radical initiator (e.g., a platinum complex catalyst)catalyzes vinyl addition. For example, a thermal free-radical initiatormay be used to crosslink unreacted vinyl groups remaining which have notreacted with a thiol group, or to react vinyl groups with otheravailable functional groups such as, but not limited to, methyl orhydroxyl groups. When a thermal free-radical initiator is used, athermal post-cure after 3D printing may be done, such as by heating thepreceramic polymer structure up to 300° C.

The thermal free-radical initiator may be selected from the groupconsisting of benzoyl peroxide, dicumyl peroxide,2,2′-azobisisobutyronitrile, platinum-carbonyl-cyclovinylmethylsiloxanecomplex, platinum-divinyltetramethyldisiloxane complex, and combinationsthereof. A combination of different types of thermal free-radicalinitiators may be employed.

The thermal free-radical initiator, when included, may be present in aconcentration from about 0.001 wt % to about 10 wt % in the composition.In various embodiments, the thermal free-radical initiator is in aconcentration of about 0.001, 0.01, 0.1, 1, 2, or 5 wt % of thecomposition.

The composition may comprise a cationic photoinitiator or photoacidgenerator, such as a sulphonium, iodonium, or ferrocenium cation pairedwith a non-nucleophilic anion, creating an onium salt. The salt, underlight exposure, creates Brønsted acids under by cleavage of thesulphonium, iodonium, and ferrocenium cation of the onium salt. Cationicphotoinitiators are typically active under wavelengths from 200 nm to350 nm. Initiators that are active at higher wavelengths are applicable.

Examples of cationic photoinitiators include, but are not limited to,sulfonium-iodonium-ferrocenium salts, cyclopentacienylcumene-ironhexafluoro phosphate, diphenyliodonium phosphate, triarylsulfoniumhexafluoroantimonate, or a combination thereof.

The cationic photoinitiator, when included, may be present in aconcentration from about 0.001 wt % to about 10 wt % in the composition.In various embodiments, the cationic photoinitiator is in aconcentration of about 0.001, 0.01, 0.1, 1, 2, or 5 wt % of thecomposition. Again, a combination of cationic photoinitiators may beemployed, or a combination of different types of initiators (e.g.,free-radical photoinitiators, cationic photoinitiators, and/or thermalfree-radical initiators).

A hydrogen donor may be used to assist in the generation of a Brønstedacid in the cation or in acceleration of anionic photoinitiatorreactions, for example. Hydrogen donors may include tertiary amines,alcohols, ethers, esters, water, or a combination thereof.

UV sensitizers may be used to enable the long UV-wavelength reaction ofUV systems with photoinitiators that typically absorb at lowerwavelengths. This is typically the case with cationic photoinitiators,which are sometimes limited to absorption at about 355 nm. UVsensitizers interact with UV light at higher wavelengths, generally intothe 400-500 nm range, and then interact with the photoinitiator tocreate free radicals and/or Brønsted acids. A UV sensitizer forms anexcited triplet state under UV light absorption, and then, throughelectron or energy transfer, reacts with a photoinitiator to generatefree radicals and/or Brønsted acids, thereby initiatingphotopolymerizaton. UV sensitizers include, but are not limited to,dibutoxyantracene, diethoxyanthracene, 1-chloro-4-propoxythioxanthone,2-isopropylthioxanthone, 4-isopropylthioxanthone, or a combinationthereof.

The UV sensitizers, when included, may be present in a concentrationfrom about 0.001 wt % to about 5 wt % in the composition. In variousembodiments, the cationic photoinitiator is in a concentration of about0.001, 0.01, 0.1, 1, or 2 wt % of the composition.

In some embodiments, the composition further comprises a free-radicalinhibitor, such as an antioxidant. A free-radical inhibitor may be addedto inhibit unwanted polymerization of regions outside the desiredprinting area, to allow sufficient resolution to the desired part, forexample. A free-radical inhibitor can also deter shadow curing, which isnormally not desired. Additionally, a free-radical inhibitor can improvelong-term stability of the formulation and keep reaction kineticparameters constant over time.

Exemplary free-radical inhibitors include, but are not limited to,hydroquinone, methylhydroquinone, ethylhydroquinone,methoxyhydroquinone, ethoxyhydroquinone, monomethylether hydroquinone,propylhydroquinone, propoxyhydroquinone, tert-butylhydroquinone,n-butylhydroquinone, N-nitroso-N-phenylhydroxylamine aluminum salt (oranother effective salt thereof), or combinations thereof.

The free-radical inhibitor, when included, may be present in aconcentration from about 0.001 wt % to about 10 wt %, typically up toabout 1 wt %, in the composition. In various embodiments, thefree-radical inhibitor is in a concentration of about 0.001, 0.005,0.01, 0.05, 0.1, 0.2, 0.5, 1, or 2 wt % of the composition.

A “3D-printing resolution agent” is a compound that improves printquality and resolution by containing the curing to a desired region ofthe laser or light exposure. In certain embodiments, a 3D-printingresolution agent functions by absorbing light (e.g., UV or visiblelight) at a desired wavelength and converting the energy either intothermal energy or radiation at a higher wavelength. The use of a3D-printing resolution agent can improve 3D-print quality and resolutionby containing the curing to the region of the laser or light exposurethat is the desired region laterally and/or vertically in the printbath.

The composition may comprise a 3D-printing resolution agent selectedfrom the group consisting of UV absorbers, fluorescent molecules,optical brighteners, and combinations thereof. Exemplary 3D-printingresolution agents include, but are not limited to,2-(2-hydroxyphenyl)-benzotriazole; 2-hydroxyphenyl-benzophenones;2-hydroxyphenyl-s-triazines;2,2′-(2,5-thiophenediyl)bis(5-tert-butylbenzoxazole);2,2′-(1,2-ethenediyl)bis(4,1-phenylene)bisbenzoxazole; or a combinationthereof.

When present, the 3D-printing resolution agent may be up to about 10 wt% of the composition, such as about 0.001, 0.01, 0.1, 0.5, 1, 2, 3, 4,5, 6, 7, 8, or 9 wt % of the composition.

In certain embodiments, the composition further comprises from about 0.1vol % to about 70 vol % of solid-phase fillers. These embodiments arediscussed in more detail, below.

Other variations of the invention provide a method of making apreceramic radiation-curable resin composition, the method comprising:

-   -   (a) obtaining a first material containing first molecules        comprising at least one Si—C bond, at least one Si—N bond, or at        least one Si—C bond and at least one Si—N bond, wherein at least        one of the first molecules comprises a repeat unit with one or        more silyl hydride groups (Si—H) available for hydrosilylation;    -   (b) obtaining a second material containing second molecules with        at least one unsaturated carbon-carbon double bond attached to        an R₄ group (R₄—C═C), and/or at least one carbon-carbon triple        bond attached an R₄ group (R₄—C≡C), wherein R₄ is a UV-active        functional group; and    -   (c) reacting, via hydrosilylation in the presence of a        homogeneous or heterogeneous metal-containing catalyst, the        first material with the second material, to generate a third        material containing third molecules comprising at least one Si—C        bond, at least one Si—N bond, or at least one Si—C bond and at        least one Si—N bond, wherein the third molecules further        comprise a R₄—C—C—Si sequence and/or a R₄—C═C—Si sequence as a        hydrosilylation reaction product.

In steps (a) and (b), “obtaining” may mean that the first or secondmolecules are obtained from a commercial source, or that the first orsecond molecules are produced from starting components.

Note that the first and second molecules may be reacted directlyfollowing generating them or otherwise obtaining them. Alternatively, oradditionally, the first and second molecules may be stored for a periodof time prior to later reacting them to produce the third molecules. Thefirst and second molecules may be separately stored (i.e., in separatecontainers) or may be combined and stored together, as a formulation tobe later converted to a preceramic radiation-curable resin composition.The location of making or obtaining the first and/or second moleculesmay be the same as, or different than, the location of reacting thefirst and second molecules to make the third molecules.

Step (c) may be conducted at a temperature from about 10° C. to about125° C., for about 10 minutes to about 48 hours, such as about 1-4hours, for example. In various embodiments, step (c) may be conducted ata temperature of about 20° C., 30° C., 40° C., 50° C., 60° C., 70° C.,80° C., 90° C., 100° C., 110° C., or 120° C. In various embodiments,step (c) may be conducted for a reaction time of about 1, 2, 3, 4, 5,10, 15, 20, 25, or 30 hours. There is generally an inverse kineticrelationship between time and temperature, such that lower temperaturesrequire longer reaction times, and vice-versa.

In preferred methods, the molar ratio of the second molecules to thefirst molecules is selected from about 1 to about n, wherein n is theaverage number of silyl hydride groups present in the first molecules,i.e., the number of individual Si—H bonds within the entire polymerchain. When the molar ratio of the second molecules to the firstmolecules is equal to 1, there is an average of only one second moleculefor each first molecule. When the molar ratio of the second molecules tothe first molecules is equal to n, there is an average of one secondmolecule for each repeat unit of the polymer chain of the firstmolecule. As an example, when n=100 and the molar ratio of the secondmolecules to the first molecules is equal to n, then 100 secondmolecules react with each first molecule. In this case, if each repeatunit of the first molecule contains one Si—H group, then one secondmolecule reacts with each repeat unit of the first molecule.

In certain methods, there is an excess of second molecules in thereaction pot, so that a mixture may be provided in which the molar ratioof the second molecules to the first molecules is larger than n, such as2n, 3n, or more. In other certain (less-preferred) methods, there isless than one hydrosilylation reaction of second molecules per firstmolecule, in which case the molar ratio of the second molecules to thefirst molecules is less than 1, such as 0.5, 0.1, or less.

Note that the first and second molecules may be reacted directlyfollowing generating them or otherwise obtaining them. Alternatively, oradditionally, the first and second molecules may be stored for a periodof time prior to later reacting them to produce the third molecules. Thefirst and second molecules may be separately stored (i.e., in separatecontainers) or may be combined and stored together, as a formulation tobe later converted to a preceramic radiation-curable resin composition.The location of making or obtaining the first and/or second moleculesmay be the same as, or different than, the location of reacting thefirst and second molecules to make the third molecules.

In some embodiments, step (c) is carried out in an inert atmosphere. Forexample, an inert atmosphere may be achieved and maintained usingvacuum, an inert gas manifold system, or in a glove box filled with aninsert gas such as helium, nitrogen, or argon.

In some embodiments, step (c) is carried out with a metal-containingcatalyst. The metal-containing catalyst may be a homogeneous catalyst,wherein the catalyst is soluble or suspended in a liquid solution ofreactants. The metal-containing catalyst may be dissolved or suspendedin a solvent, such as hexane, cyclohexane, toluene, furan,tetrahydrofuran, methyltetrahydrofuran, methylpyrrolidine, pyridine,chloroform, or a combination thereof.

The metal-containing catalyst may be a heterogeneous catalyst, whereinthe catalyst is in a different phase than the reactants. Typically, aheterogeneous catalyst is in a solid phase and reactants are in a liquidor vapor phase. Heterogeneous catalysts may be supported on a catalystsupport, such as silica, alumina, silicates, aluminosilicates, zeolites,or carbon, for example. Mesoporous silica in the form of MCM-41 orSBA-15 may be used, in certain embodiments.

Metal-containing catalysts (whether homogeneous or heterogeneous) mayinclude metal complexes of the form M-L, wherein M is selected from thetransition metals (e.g., Pt, Pd, Ru, Rh, Ni, and/or Co), and wherein Lis a ligand selected from halides, alkyl groups, aryl groups,aliphatically unsaturated groups, organosilicon groups, carbon monoxide,or a combination thereof.

Exemplary metal-containing catalysts include, but are not limited to,chloroplatinic acid hydrate (Speier's catalyst),platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex solution(Karstedt's catalyst),benzylidenebis(tricyclohexylphosphine)dichloro-ruthenium(II),tris(triphenylphosphine)rhodium(I) chloride,dichloro(1,5-cyclooctadiene)platinum(II), platinum supported on silica,platinum supported on alumina, platinum supported on activated carbon,Pt/MCM-41, Pt/SBA-15, or a combination thereof.

The metal-containing catalyst may be present from about 0.00001% (0.1ppm) to about 5% by weight of the reaction mixture. In some embodiments,the preceramic resin precursor formulation contains no catalyst, such aswhen uncatalyzed hydrosilylation is utilized.

A solvent may be employed in the reaction mixture for step (c), todissolve or suspend the first and second molecules to be reacted. Forexample, an aprotic organic solvent may be utilized, such as (but notlimited to) hexane, cyclohexane, toluene, diethyl ether,tetrahydrofuran, 2-methyltetrahydrofuran, pyridine, n-methylpyrrolidine,chloroform, or a combination thereof. In various embodiments, thesolvent is present in a concentration of about 10, 20, 30, 40, 50, 60,70, 80, or 90 wt % of the reaction mixture.

In some embodiments, step (c) is carried out with an inhibitor present,such as to inhibit premature polymerization. Inhibitors may befree-radical inhibitors, cationic polymerization inhibitors,hydrolsilylation inhibitors, or another type of inhibitor. Inhibitorsmay include, but are not limited to, hydroquinones such astert-butylhydroquinone, methylhydroquinone, ethylhydroquinone,methoxyhydroquinone, ethoxyhydroquinone, monomethylether hydroquinone,propylhydroquinone, propoxyhydroquinone, and n-butylhydroquinone.Inhibitors may alternatively, or additionally, include1,3-divinyltetramethyldisiloxane,1,3,5,7-tetravinyl-1,3,5,7-tetra-methylcyclotetrasiloxane,N-nitroso-N-phenylhydroxylamine aluminum salt, or a combination thereof.The inhibitor(s) may be in a concentration from 0 wt % to about 5 wt %of the reaction mixture, for example.

The “reaction conversion” is the extent of reaction of first and secondmolecules into third molecules, based on the stoichiometrically limitingreactant. In the case of stoichiometric amounts of both reactants (firstmolecules and second molecules), the reaction conversion may be based oneither of the reactants. In various embodiments, the reaction conversionis at least 50%, 75%, 90%, 95%, or 99%. Preferably, the reactionconversion is at least 90%, at least 95%, or essentially 100%.

The “reaction selectivity” is the selectivity of the reaction toward thedesired third molecules, versus side products. In the case of perfectlystoichiometric conversion of first molecules and second molecules intothird molecules, the reaction selectivity is 100%, even if there is anexcess of one of the reactants or if the reaction conversion is lessthan 100%. In various embodiments, the reaction selectivity is at least50%, 75%, 90%, 95%, or 99%. Preferably, the reaction selectivity is atleast 90%, at least 95%, or essentially 100%.

Reaction selectivity and reaction conversion are thus separateparameters. Reaction conversion is typically dictated by kineticparameters such as time, temperature, and the presence of a catalyst,for example, while reaction selectivity may be influenced by the natureof the starting molecules, impurities present (if any), and the kineticsof side reactions compared to the desired main reaction. “Reactionyield” is reaction conversion x reaction selectivity. In variousembodiments, the reaction yield is at least 25%, 50%, 75%, or 90%.Preferably, the reaction yield is at least 80%, at least 90%, oressentially 100%.

The reaction in step (c) is carried out in a reactor, which may beagitated or non-agitated. Agitation enhances mass and heat transfer.Step (c) may be conducted as a batch, continuous, or semi-continuousprocess. When the reaction is continuous or semi-continuous, the flowpattern in the reactor may be plug flow, continuously stirred, orbetween these extremes.

The method may further include purifying the third material, after thedesired reaction conversion is achieved. Purification may includeremoving solvent (if used), unreacted starting molecules (if any), andresidual inhibitors (if any). Purifying may be accomplished bysolvent/solvent extraction, evaporation (e.g., via a rotary evaporator,or “rotovap”), distillation, vacuum distillation, chromatography,filtration (such as with activated carbon or silica gel),centrifugation, or a combination thereof. Other purification techniquesmay be employed to separate and recover the third material for storageor further use.

The third material may be combined with a catalyst quencher to captureor poison the metal-containing catalyst. For example, the product fromthe hydrosilylation is optionally treated with a catalyst quencher atroom temperature, to inhibit premature curing.

The weight ratio of the catalyst quencher to the active metal in themetal-containing catalyst may be from about 0.001 to about 10, such asabout 0.01, 0.1, 0.5, 1, 2, 3, or 5, for example.

In some embodiments, the catalyst quencher is selected from the groupconsisting of activated carbon, dimethyl maleate, dimethyl fumarate,benzothiazole, triphenylphosphine, and combinations thereof. Othermolecules containing conjugated double bonds, thiazole groups, and/orphosphine groups may be employed as catalyst quenchers.

As mentioned earlier, the preceramic composition may further comprise asolid metal filler and/or a solid ceramic filler. Solid fillers may beadded after the preceramic radiation-curable resin composition isproduced. Alternatively, or additionally, solid fillers may be added tothe starting formulation so that they remain present in the preceramiccomposition generated (via hydrolsilylation) from the startingformulation.

A solid ceramic filler or solid metal filler is a ceramic or metalmaterial that (a) forms at least one solid phase at 25° C. and 1 atm,and (b) enhances at least one chemical, physical, mechanical, orelectrical property within the preceramic composition or a reactionproduct thereof.

In some embodiments, the preceramic composition comprises a solid metalfiller that has a melting temperature equal to, or greater than, thepyrolysis temperature of a polymerized variant of the liquid resin. Inthese or other embodiments, the preceramic composition comprises a solidmetal filler that has a melting temperature less than the pyrolysistemperature of a polymerized variant of the liquid resin. The meltingtemperature of a solid metal filler may be about 200° C., 300° C., 400°C., 500° C., 600° C., 700° C., 800° C., 900° C., 1000° C., 1100° C.,1200° C., 1300° C., 1400° C., 1500° C., or higher, for example.

The solid ceramic or metal filler may be from about 0.1 vol % to about70 vol % of the preceramic composition, with the majority of theremainder typically being the liquid resin and the solid polymer filler.

The geometric shape of the solid ceramic or metal filler may be fibersincluding short fibers (1-100 micrometers in length) or long fibers(>100 micrometers in length), whiskers, nanotubes, nanorods, flatplatelets, microparticles with diameters between 1 and 100 micrometers,nanoparticles with diameters between 1 and 1000 nanometers, or acombination thereof.

In some embodiments, to increase fracture toughness of a 3D-printedpart, solid ceramic or metal fillers with aspect ratios of at least 2are preferred, such as fibers, whiskers, nanotubes, and nanorods. Here,“aspect ratio” is the ratio of average length to average width, or inthe case of an arbitrary shape, the ratio of average maximum lengthscale to average minimum length scale. The solid ceramic or metal filleraspect ratio is preferably at least 5, more preferably at least 10, incertain embodiments.

The solid ceramic or metal filler is preferably stable at a pyrolysistemperature of at least 800° C., so as not to disintegrate, melt, orvaporize during later conversion of a preceramic polymer to a ceramicmaterial. Note that the solid ceramic or metal filler may react atpyrolysis temperatures with other components present in the preceramiccomposition or its reaction products (e.g., preceramic polymer) or withfurnace atmosphere gases. It is possible for a portion of the solidceramic or metal filler to react away into the vapor phase, or into aliquid phase, during high-temperature processing.

In certain embodiments, a solid ceramic or metal filler precursor isintroduced to the preceramic composition, wherein the precursor is in aliquid phase or is a gel, for example. The precursor may then react orundergo a phase change, such as during polymerization, to convert theprecursor into a solid ceramic or metal filler.

The optional solid ceramic or metal filler may have a wide range ofcompositions. For example, solid ceramic or metal filler compositionsmay include, but are not limited to, silicon-based ceramics such asSiOC, SiO₂, SiCN, SiC, SiCBN, SiOCN, Si₃N₄, silicate glasses, etc. Solidceramic or metal filler compositions may include non-silicon-basedceramics such as metal oxides, e.g. Al₂O₃, ZrO₂, TiO₂, or Y₃Al₅O₁₂.Solid ceramic or metal filler compositions may include carbide-basedceramics such as carbon, graphene, diamond, and metal carbides, e.g.TiC, ZrC, HfC, or B₄C. Solid ceramic or metal filler compositions mayinclude nitride-based ceramics, e.g. BN, TiN, ZrN, AlN, or Si₃N₄. Solidmetal filler compositions may include pure metals or metal alloys, suchas (but not limited to) alkali metals, alkaline earth metals, transitionmetals, post-transition metals, or combinations or alloys thereof.

Solid ceramic or metal fillers in a resin interact with UV lightaccording to Snell's law and the well-known Fresnel equations. Theselaws of physics determine the fractions of the light that are reflected,transmitted, or absorbed when UV light passes from resin to filler. Fora UV-based 3D printing process, it is preferred that the solid fillersdo not absorb too much UV light which would hinder complete UV curing ofthe resin.

To avoid absorption of too much UV light, a low level of solid ceramicor metal filler (if any) may be employed, such as less than 10 vol % ofrelatively small (e.g., 10 micron or smaller) particles. Alternatively,or additionally, a solid ceramic or metal filler that is somewhattransparent to UV light and lets UV light pass through, may be employed.

Another approach to ensure that UV light is not excessively absorbed bythe filler particles is to employ solid particles with a surface thatreflects UV light. For example, aluminum reflects UV light well. Formaximum reflection, the surface of such particle should be smooth.Surface treatments or coatings may be applied to render the surface offiller particles reflective—such as a thin coating of aluminum orsilver.

Preferred solid ceramic or metal filler materials, in some embodiments,are short fibers of alumina (Al₂O₃), quartz (SiO₂), glass, siliconnitride (Si₃N₄), yttrium aluminum garnet (YAG), or boron nitride (BN)because these materials transmit at least some UV light. SiC or C fibersabsorb significant UV light and therefore should be coated with areflective coating, to enable efficient 3D printing.

In some variations, active solid-phase functional additives areincluded. By “solid-phase functional additives” it is meant a materialthat (a) forms at least one solid phase at 25° C. and 1 atm, and (b)performs or enhances at least one chemical, physical, mechanical, orelectrical function within the ceramic structure as it is being formedand in the final structure.

Note that the optional solid-phase functional additives aredistinguished from the solid ceramic or metal fillers disclosed above.Compared to solid fillers, solid-phase functional additives activelyimprove the final ceramic structure through one or more changesexplicitly induced by the additives during pyrolysis or other thermaltreatment, as will now be described.

The solid-phase functional additives may be present from about 0.1 vol %and 70 vol % of the preceramic composition. The solid-phase functionaladditive geometry varies. In some embodiments, the solid-phasefunctional additives are small particles with average sizes (length oreffective diameter) from 5 nanometers to 5 micrometers.

In some embodiments, the solid-phase functional additives activelyexpand in volume and counteract the shrinkage of the resin, eliminatingor reducing the overall shrinkage during conversion of the polymer toceramic.

On conversion from polymer to ceramic, typically about 20-30% lineardimensional shrinkage and about 20-60% mass loss are observed. Theshrinkage facilitates cracking and distortion, and limits the achievablepart size and tolerances. By introducing active solid-phase functionaladditives that expand in volume during pyrolysis, the shrinkage of thepreceramic polymer is counteracted. The overall shrinkage duringconversion of the polymer to ceramic can be reduced or even eliminated.

Note that the solid-phase functional additives are not necessarilystable (unreactive) at pyrolysis temperatures. In many case, it isdesired that the functional additives are reactive.

In particular, the solid-phase functional additives may react with thepreceramic composition directly on heat treatment. Alternatively, oradditionally, the solid-phase functional additives may react withspecies (e.g., oxygen, nitrogen, or carbon) generated from decompositionof the preceramic polymer during pyrolysis.

Alternatively, or additionally, the solid-phase functional additives mayreact with the pyrolysis atmosphere during the pyrolysis, for examplewith a nitrogen, methane, or ammonia atmosphere. To counteract thedetrimental effects of shrinkage, it is preferred that these reactionshappen at the same time as the preceramic polymer shrinks, or areeffective to reverse the volume reduction.

Examples of solid-phase functional additives for counteracting theshrinkage of the preceramic polymer include, but are not limited to,scandium, yttrium, titanium, zirconium, hafnium, vanadium, niobium,tantalum, chromium, molybdenum, tungsten, manganese, iron, cobalt,nickel, zinc, boron, aluminum, gallium, silicon, germanium, phosphorus,or combinations thereof. Combinations of these elements such as titaniumsilicide, chromium silicide, magnesium silicide, zirconium silicide, ormolybdenum silicide may be used as the solid-phase functional additives.Preferred solid-phase functional additives in this category includealuminum, titanium, zirconium, titanium silicide, chromium silicide,magnesium silicide, and zirconium silicide.

In some embodiments, the solid-phase functional additives actively seedcrystallization of a preferred ceramic phase by enabling epitaxialgrowth of the preferred phase without a nucleation barrier. Afterpyrolysis of preceramic polymers, an amorphous ceramic is usuallyobtained. To increase strength and hardness, and reduce high-temperaturecreep, the amorphous ceramic material needs to then be crystallized intoa preferred ceramic phase. This is typically achieved by a long (manyhours) heat treatment at temperatures above the pyrolysis temperature,performed right after the pyrolysis or as a distinct second heattreatment.

By contrast, with appropriate solid-phase functional additives,crystallization may be facilitated by seeding crystallization. Withoutlimitation, the mechanism may include providing a surface for epitaxialgrowth of the preferred phase or multiple ceramic phases.

For example, the crystallization of β-SiC in an amorphous SiC or SiCNceramic derived from a polycarbosilane-based or polysilazane-based resincan be facilitated by small (e.g., 1 nanometer to 5 microns) β-SiCcrystals. Crystallization of such a resin may be performed attemperatures between 1300° C. and 2800° C. over the course of 5 to 50hours. Similarly, the crystallization of the a phase or 13 phase ofSi₃N₄ in an amorphous Si₃N₄ or SiCN ceramic derived from apolysilazane-based resin can be facilitated by small (e.g., 50nanometers to 5 microns) β-Si₃N₄ or β-Si₃N₄ crystals, respectively.Other crystals may be chosen to facilitate crystallization, with thetypical constraint of epitaxial growth on one crystal facet with lowlattice strain.

In the above or other embodiments, the preceramic composition mayinclude a solid polymer filler present at a concentration from about 0.1vol % to about 95 vol % of the preceramic composition, such as fromabout 1 vol % to about 70 vol % of the preceramic composition. Invarious embodiments, the solid polymer filler is at a concentration ofabout 0.5, 1, 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, or 90 vol % of thepreceramic composition.

The solid polymer filler may be an organic polymer, an inorganicpolymer, or a combination thereof. In certain embodiments, the solidpolymer filler is a silicon-based polymer. In other certain embodiments,the solid polymer filler is a boron-based polymer. Mixtures of more thanone type of solid polymer filler may be present.

The solid polymer filler may be selected from the group consisting ofpoly(carbosilanes), poly(silazanes), poly(silsesquioxanes),poly(borosiloxanes), poly(borosilanes), poly(borosilazanes),poly(carbosiloxanes), poly(silylcarboimides),poly(silsesquicarbodiimides), polyborazines, and combination thereof.The solid polymer filler is preferably fully polymerized, but in someembodiments, some uncured monomer may be present (e.g., carbosilanes,silazanes, etc.) along with cured polymer.

When the solid polymer fillers are themselves preceramic polymers, theymay be converted upon thermal treatment to various ceramic materialsincluding, but not limited to, silicon oxycarbide (SiOC), siliconcarbide (SiC), silicon nitride (Si₃N₄), silicon oxynitride (SiON),silicon carbonitride (SiCN), silicon boronitride (SiBN), silicon boroncarbonitride (SiBCN), boron nitride (BN), silicon metal carbides,silicon metal oxides, silicon metal nitrides, graphite, diamond, or acombination thereof.

In some embodiments, the solid polymer filler is an inorganic polymercharacterized by a pyrolysis temperature equal to, or greater than, thepyrolysis temperature of a polymerized variant of the liquid resin. Inother embodiments, the solid polymer filler is an organic or inorganicpolymer characterized by a pyrolysis temperature less than the pyrolysistemperature of a polymerized variant of the liquid resin. A “polymerizedvariant” of the liquid resin means the polymer obtained by polymerizingor curing the liquid resin.

The “pyrolysis temperature” of a polymer is defined herein as theminimum thermal decomposition temperature from thermogravimetricanalysis of a 10-milligram sample in a nitrogen atmosphere at a 10°C./min heating rate, as described in Beyler and Hirschler, “ThermalDecomposition of Polymers” SFPE Handbook of Fire Protection Engineering2, Section 1, Chapter 7, pages 111-131, 2002, which is herebyincorporated by reference herein. Note that the pyrolysis temperature ofa polymer is a property of that polymer, similar to polymerglass-transition temperature, without reference to how the polymer ismade or used.

In various embodiments, the pyrolysis temperature of the solid polymerfiller is about, at least about, or at most about 100° C., 150° C., 200°C., 250° C., 300° C., 350° C., 400° C., 450° C., or 500° C.

In various embodiments, the pyrolysis temperature of the polymerizedvariant of the liquid resin is about, at least about, or at most about100° C., 150° C., 200° C., 250° C., 300° C., 350° C., 400° C., 450° C.,or 500° C.

When it is desired to actually pyrolyze a solid polymer filler, thepolymerized liquid resin, or both of these, the preceramic compositioncontaining the solid polymer filler should be subjected to a reactiontemperature at least equal to the pyrolysis temperature of theapplicable polymer, and preferably higher than its pyrolysistemperature, for some period of time.

The solid polymer filler may itself be an inorganic, cured preceramicpolymer. In some of these embodiments, the solid polymer filler has thesame composition as a polymerized variant of the liquid resin. In otherembodiments, the solid polymer filler has a different composition than apolymerized variant of the liquid resin. Some embodiments provide apreceramic liquid resin formulation—suitable for making a firstpreceramic polymer—mixed with a dispersed solid phase containing asecond preceramic (cured) polymer that is different than the firstpreceramic polymer.

The solid polymer filler may be dispersed within the composition as aslurry, an emulsion, a solid solution, or some other form of dispersion.In some embodiments, a portion of solid polymer filler is well-dispersedwithin the liquid resin while the remainder is non-dispersed, such as inthe form of precipitated or agglomerated solid polymer filler.Preferably, at least 80 wt %, more preferably at least 90 wt %, and mostpreferably at least 95 wt % or at least 99 wt % (such as essentiallyall) of the solid polymer filler is well-dispersed within the liquidresin.

“Well-dispersed” solid polymer filler means that individual particles ofsolid polymer filler are uniformly (homogeneously) distributed in spacewithin the liquid resin. Well-dispersed solid polymer filler leads touniform shrinkage during pyrolysis. Common methods to analyze thedispersion of particles include optical microscopy, scanning electronmicroscopy, transmission electron microscopy, and ultraviolet-visible(UV-Vis) spectroscopy. Tyson et al., “A quantitative method foranalyzing the dispersion and agglomeration of nano-particles incomposite materials” Composites Part B: Engineering Volume 42, Issue 6,September 2011, Pages 1395-1403, is hereby incorporated by referenceherein for its teachings of quantifying dispersions of particles.

Dispersion of solid polymer filler within the liquid resin may beachieved for example by a mechanical process of mixing polymer andfiller, wherein shear forces are applied to the mixture. Ultrasonicmixing may also be employed. Settling of solid polymer filler particlesmay be minimized by optimization of particle size, adjustment toviscosity of the liquid resin, and/or control of mixing conditions suchas temperature.

The particle size of the solid polymer filler may vary widely. In someembodiments, the solid polymer filler has an average particle size(e.g., diameter, effective diameter, or length) from about 1 nanometerto about 1000 microns, such as about 10, 50, 100, 200, 300, or 500nanometers, or about 1, 10, 50, 100, 200, 300, or 500 microns. Evenlarger particle sizes may be used for the solid polymer filler, such asabout 1, 2, 3, 4, 5 millimeters or more.

Particles sizes may generally be measured by a variety of techniques,including dynamic light scattering, laser diffraction, image analysis,or sieve separation, for example. Dynamic light scattering is anon-invasive, well-established technique for measuring the size and sizedistribution of particles typically in the submicron region, and withthe latest technology down to 1 nanometer. Laser diffraction is a widelyused particle-sizing technique for materials ranging from hundreds ofnanometers up to several millimeters in size. Exemplary dynamic lightscattering instruments and laser diffraction instruments for measuringparticle sizes are available from Malvern Instruments Ltd.(Worcestershire, England). Image analysis to estimate particle sizes anddistributions can be done directly on photomicrographs, scanningelectron micrographs, or other images. Finally, sieving is aconventional technique of separating particles by size.

The geometric shape of the solid polymer filler may vary widely. In someembodiments, the solid polymer filler is in the form of powders (i.e.fine particles), short fibers (e.g., with length of 1-100 microns), longfibers (e.g., with length of 100-1000 microns), whiskers, nanotubes,nanorods, flat platelets, or a combination thereof. A combination offiller shapes may be used to increase dispersion in the resin and modifycompositional phase distribution of the 3D-printed part.

The use of solid polymer fillers that are only partially cured or in agreen state enables the reaction or crosslinking between theradiation-curable liquid resin and the solid polymer filler, providingrobust cured polymer parts with higher mass retention, in someembodiments.

In some embodiments, the method further comprises 3D printing andthermally treating the preceramic radiation-curable resin composition togenerate a ceramic material.

The extremely high melting point of many ceramics poses a challenge toadditive manufacturing to make a 3D part, as compared with metals andpolymers. Ceramics cannot be cast or machined easily. By contrast, thepresent methods enable geometrical flexibility. As described herein,preceramic resins that are cured with ultraviolet (UV) light in astereolithography 3D printer or through a patterned mask, for example,form 1D, 2D, or 3D polymer structures that can have complex shape andcellular architecture. These polymer structures can then be thermallyconverted to the corresponding 1D, 2D, or 3D ceramic part, preferablywith low shrinkage, or at least uniform shrinkage.

The preceramic monomer formulations are designed to allow the ceramicstructures to be formed with preferably high thermal stability (such aschemical and physical stability at temperatures greater than 1500° C.)and good mechanical strength (including stiffness, flexural strength,hardness, and/or fracture toughness).

The compositions disclosed herein may be 3D-printed using many differentmethods. In some variations, the compositions may be directly 3D-printedand converted to free-form ceramic matrix composite structures. A3D-printed preceramic polymer material may be prepared directly frompreceramic compositions, with no intervening steps being necessary. A3D-printed ceramic material may then be prepared directly from the3D-printed preceramic polymer material, with no intervening steps beingnecessary.

Typically, a preceramic composition is conveyed (printed) to a region ofinterest, such as via stereolithography, binder jetting, resin jettingwith fiber placement, polyjetting, or extrusion printing, eitherfollowed by polymerization or with polymerization taking placesimultaneously with the printing. Preferably, the polymerizing and 3Dprinting steps are performed simultaneously, at a desired location(e.g., a layer) within a part. In some embodiments, the polymerizing and3D printing steps are performed semi-simultaneously, in which multiplesteps are performed overall while at each step, some amount ofpolymerizing and some amount of 3D printing takes place. In someembodiments, a preceramic resin is first polymerized, followed by 3Dprinting of the already-made polymer (e.g., a thermoplastic material).

In stereolithography, layers of resin composition are cured from the topor bottom using UV-laser rastering, projection micro-stereolithography,digital light projection, or liquid crystal device projection, forexample. Smaller filler sizes are preferred since the filler size oftenlimits the resolution, depending on material choice.

Generally speaking, “jetting” of a material means that droplets of abuild material are selectively deposited onto a build bed to develop athree-dimensional object. Jetting can be carried out by liquiddeposition, vapor deposition, or liquid-vapor mist deposition, forexample, via spraying (such as via a nozzle in communication with amaterial under pressure), impingement (such as via a tube or pipe incommunication with a material that is pumped), or other means.

In binder jetting, a layer of liquid resin is jetted on selectedlocations and cured such as via UV light or thermally. This process issimilar to conventional binder jetting methods, but instead of a binder,a preceramic composition is used. An optional solid filler may initiallybe spread out on a substrate or on a region of polymer based on theselected monomer, if desired. After an initial step of binder jetting,another layer is generated via resin jetting and curing. This processmay be repeated many times for large parts.

In resin jetting with fiber placement, solid fillers in the form of longor short fibers are placed in the preferred location and aligned in thepreferred direction. Subsequently, liquid resin is jetted in selectedlocations and cured. The process is repeated layer-by-layer to build apart. Resin jetting with fiber placement enables printing of parts withhigh volume fraction (such as 30-60 vol %) of aligned fibers, resultingin improved mechanical properties for the final ceramic structure(following pyrolysis).

In polyjetting, a mixture of liquid resin (and optionally solid fillers)is jetted and written into the desired pattern. As the mixture isdispensed, it is exposed to UV light such as a laser, LED, or plasmasources, and cured into a polymer. Multiple mixtures are able to bedispensed through different nozzles, allowing for more than onecomposition to be utilized simultaneously. This results in tailoredmechanical properties for the final ceramic structure (followingpyrolysis).

In extrusion printing, the liquid resin composition is squeezed througha micro-nozzle, or multiple micro-nozzles, and cured via UV light. Oneadvantage is that high-aspect-ratio fillers can be aligned with theextrusion process. Alignment generally improves mechanical properties inthe aligned direction.

After a part is 3D printed using any of the above methods, or anothermethod, the part may be post-cured. An optional thermal post-cure of the3D polymer is performed after the 3D printing but prior to the pyrolysisto produce the ceramic structure. A post-cure step may be employed tocrosslink unreacted functional groups, for example. Post-curing may beaccomplished by additional UV exposure and/or a thermal post-cure atelevated temperatures (such as 60-500° C.) in an oven for about 10minutes to about 8 hours. When a thermal post-cure is to be done, it canbe beneficial to include a thermal initiator in the initial 3D-printingcomposition, to facilitate later thermal curing.

In some embodiments, the curing or conversion of the preceramiccomposition to a preceramic polymer includes crosslinking. A crosslinkis a bond that links one polymer chain to another. Crosslink bonds canbe covalent bonds or ionic bonds. When polymer chains are linkedtogether by crosslinks, they lose some of their ability to move asindividual polymer chains. Crosslinks are the characteristic property ofthermosetting plastic materials. In most cases, crosslinking isirreversible, unless ionic bonds are employed in reversible crosslinks.See, for example, commonly owned U.S. patent application Ser. No.15/391,749, filed Dec. 27, 2016, which is hereby incorporated byreference herein, regarding reversible crosslinks.

In some embodiments, while a monomer is being converted to polymer, agel is formed first. Gel formation is followed by formation of a solidmaterial as the monomer conversion is further increased, to crosslinkchains together. A “gel” is a solid, jelly-like material that can haveproperties ranging from soft and weak to hard and tough. Gels exhibit noflow when in the steady-state. By weight, gels are mostly liquid, yetthey behave like solids due to a three-dimensional crosslinked networkwithin the liquid.

The direct, near-net-shape conversion of a preceramic 3D-printed polymerto a ceramic structure may be achieved by pyrolysis or other thermaltreatment, such as (but not limited to) sintering, annealing, orcalcination. Typically, the thermal treatment is based on heating the3D-printed structure for an extended period of time (such as from 10minutes to 1 week) under various inert or reactive atmospheres.

Thermal treatment may be done for an extended period of time undervarious inert or reactive atmospheres, including but not limited to N₂,Ar, He, air, CO₂, CO, H₂, CH₄, C₂H₆, C₂H₄, NH₃, or a combinationthereof. Treatment pressures may vary from about 1 atm to about 20 atm,for example. Vacuum pyrolysis may also be employed, in which thetreatment pressure is less than 1 atm, again under various atmospheresas noted above.

The pyrolysis or other thermal treatment may include heating at aheating rate of 0.1-20° C./min from ambient temperature to an elevatedtemperature from about 500° C. to about 2000° C., such as from about800° C. to about 1100° C. When it is desired to convert the polymerizedliquid resin into ceramic material, the selected temperature needs to atleast be equal to the pyrolysis temperature of the polymerized liquidresin (a polymer property defined above), and preferably greater thansuch pyrolysis temperature, such as at least 50° C., 100° C., 200° C.,300° C., 400° C., or 500° C. greater than the pyrolysis temperature ofthe polymerized liquid resin.

When it is desired to convert the solid polymer filler also into ceramicmaterial, the selected temperature needs to at least be equal to thepyrolysis temperature of the solid polymer filler, and preferablygreater than such pyrolysis temperature, such as at least 50° C., 100°C., 200° C., 300° C., 400° C., or 500° C. greater than the pyrolysistemperature of the solid polymer filler.

Slow heating rates are preferred to enable evolving gases to escape,thereby minimizing porosity in the final part. When porosity is desired,higher heating rates (e.g., higher than 20° C./min) may be employed. Thepyrolysis or other thermal treatment may also include dwelling at theelevated temperature (e.g., 950° C.) for at least 1, 5, 10, 15, 30, or60 minutes, for example. Following pyrolysis, the material may be cooledat a cooling rate (magnitude) of 0.1-20° C./min back to ambienttemperature. In some embodiments, faster cooling (e.g., higher than 20°C./min in magnitude) is desired to freeze-in a desired microstructure,for example.

The thermal treatment is preferably performed following polymerizationand any (optional) thermal post-cure of the 3D-printed polymer. Incertain embodiments, the thermal treatment is combined (i.e., overlapsin time and/or temperature) with polymerization, thermal post-cure, orboth. It will also be recognized that even when a sequential operationis intended, some amount of ceramic formation may occur prior to aplanned step of thermal treatment, as a result of the intrinsic kineticsand thermodynamics of the reaction system.

In some embodiments, a reactive thermal treatment is performed, in whichthe gas that is initially present is reactive toward the initialpolymer, the final ceramic material, or both of these. When the gas isreactive, it may react with a component and cause it to leave thematerial. Alternatively, or additionally, the gas may react with acomponent and remain with the base material. It is also possible for thegas to react and form products, some of which depart from the materialwhile the rest remains with the material. Reactive gases may be selectedfrom O₂, O₃, air, CO, CO₂, H₂, H₂O, CH₄, SO₂, H₂S, NH₃, NO, NO₂, andN₂O, and so on. The maximum temperature for reactive thermal treatmentmay be, for example, about 300° C. to about 2000° C. The system pressuremay also be adjusted to influence the gas atmosphere.

In some embodiments, a solid polymer filler and the preceramic polymer(from polymerization of the resin composition) pyrolyze in parallel toform a cohesive ceramic structure. The ceramic microstructure may behomogenous or heterogeneous. That is, regions derived from pyrolysis ofthe preceramic polymer may be heterogeneous with discrete regionsderived from pyrolysis of the solid polymer filler. Or, the finalceramic structure may be homogeneous, without discrete regions derivedfrom pyrolysis of the preceramic polymer versus those derived frompyrolysis of the solid polymer filler.

Following pyrolysis or other thermal treatment, the ceramic materialcomprises chemically and/or physically interconnected ceramic materialssuch as, but not limited to, silicon oxycarbide (SiOC), silicon carbide(SiC), silicon nitride (Si₃N₄), silicon oxynitride (SiON), siliconoxycarbonitride (SiOCN), silicon carbonitride (SiCN), siliconboronitride (SiBN), silicon boron carbonitride (SiBCN), boron nitride(BN), and/or silicon metal carbides, oxides, or nitrides. The ceramicmaterials may be interconnected in a solid solution, and/or there may bechemical bonds between individual ceramic particles. There may also bean interface layer between ceramic materials. The ceramic materials maybe interconnected within a three-dimensional structure.

The composition of the ceramic part or ceramic matrix compositeobviously is directly dependent on the composition of the startingpreceramic composition as provided in this disclosure.

In some embodiments, final ceramic structures are lightweight, strong,and stiff—but can withstand a high-temperature oxidizing environment.The configuration and microstructure of the preceramic polymer determinethe composition, microstructure, and yield of the ceramic material afterthermal treatment. A high crosslink density may be preferred to preventthe fragmentation and loss of low-molecular-mass species, which have notfully converted to either ceramic or escaping gases, during thermaltreatment.

During the thermal treatment, whether an inert or reactive thermaltreatment technique is employed, gases escape. Gases are formed duringthe conversion of preceramic polymer to the ceramic structure, bydecomposition reactions of the polymer and other materials present. Theescaping gases or vapors may include (but are by no means limited to)CH₄, H₂, CO, CO₂, H₂O, SO₂, H₂S, CH₃S, etc.

The final ceramic structure may be characterized by an actual densitythat is at least 50% of theoretical density, preferably at least 75% oftheoretical density, and more preferably at least 95% of theoreticaldensity. By “theoretical density” it is meant the density of thematerial itself, calculated in the absence of porous voids. For examplea ceramic structure with absolute density of 2.0 g/cm³, fabricated froma base material with inherent (bulk) density of 2.1 g/cm³, exhibits2.0/2.1=95% of theoretical density. In certain embodiments, withoutlimitation, the ceramic structure is a fully dense monolith, which meansthat the ceramic structure has at least 99% (e.g., essentially 100%) oftheoretical density associated with a part or continuous region ofmaterial (also referred to as a “monolith”). The absolute density ing/cm³ will vary, depending on the selection of base materials; anexemplary range is about 1 g/cm³ to about 5 g/cm³.

The overall mass loss associated with the conversion of preceramicpolymer to the ceramic structure may vary widely, such as from about 1wt % to about 90 wt %, e.g. about 5, 10, 20, 30, 40, 50, 60, 70, or 80wt %. The overall mass loss will be dictated by the starting formulation(e.g., fraction organic versus inorganic) as well as by processparameters. In principle, the lost mass may be recovered separately andused for other purposes.

Associated with mass loss may be shrinkage of the preceramic polymer asit converts to the ceramic structure. The linear shrinkage (calculatedin a single dimension, such as height of part) may be from 0% to about60%, for example. Note that the mass loss and shrinkage are notnecessarily correlated. In some embodiments with high mass loss, thereis not much (if any) shrinkage. These embodiments tend to produce higherporosity and therefore lower densities. In some embodiments with highmass loss, there is substantial shrinkage, unless certain solid-phasefillers are utilized as described above. These embodiments tend toproduce lower porosity, or no porosity, and therefore higher densities(e.g., fully dense ceramic materials). Finally, in some embodiments,there is little mass loss but shrinkage associated with chemicalreactions taking place. These embodiments also tend to producerelatively high densities.

Despite shrinkage, if any, the bulk shape (relative geometry) of thepreceramic 3D-printed polymer may be preserved in the final ceramicstructure. That is, when shrinkage is uniform in all dimensions, thegeometrical features are retained in the part: it is a scaled-downversion, in all three dimensions. In some embodiments, shrinkage isapproximately uniform, which means the geometrical features arebasically maintained, with slight deviations. Uniform shrinkage occurswhen there is no random fragmentation during conversion of thepreceramic polymer to the ceramic structure, and when the reactions andgas escape are isotropic within the material. Note that very smallfeatures, such as at the nanoscale, may not be preserved duringotherwise uniform shrinkage.

Practically speaking, uniform shrinkage (or no shrinkage, in certainembodiments employing active functional additives) enables the formationof parts that are “net shape” or “near net shape.” “Net shape” meansthat the geometrical features are retained, so that manufactured partsallow final fabrication matching the intended design with little or nopost-processing. “Near net shape” means that the geometrical featuresare not perfectly retained but require only minimal post-processing orhand-work. Both net-shape parts and near-net-shape parts require littleor no machining, polishing, bonding, surface finishing, or assembly.

The strength of the final ceramic material will vary, depending on theinitial preceramic composition, as well as the processing parameters. Insome embodiments, the final ceramic material is characterized by aYoung's Modulus of at least about 200 GPa, 300 GPa, 400 GPa, 500 GPa, ormore, measured at 25° C. In some embodiments, the final ceramic materialis characterized by a flexural strength of at least about 300 GPa, 400GPa, 500 GPa, or more, measured at 25° C. In some embodiments, the finalceramic material is characterized by a hardness of at least about 10GPa, 20 GPa, 30 GPa, or more, measured at 25° C.

The thermal stability of the final ceramic material will vary, dependingprimarily on the initial preceramic resin formulation, as well as theprocessing parameters. In various embodiments, the final ceramicmaterial is thermally stable at a temperature of at least 1500° C.,1600° C., 1700° C., 1800° C., 1900° C., or 2000° C. Thermal stabilitymeans at least that the ceramic material does melt at thesetemperatures, and preferably also that the ceramic material does notreact (e.g., by oxidation or reduction), undergo thermal shock, orphysically decompose (introducing defects) at these temperatures. Insome embodiments, for example, the ceramic structure is characterized bybeing stable in the presence of air at a temperature of about 1000° C.,1100° C., 1200° C., 1300° C., 1400° C., 1500° C., 1600° C., 1700° C.,1800° C., or higher.

Multiple ceramic structures may be obtained and then joined, usingmethods such as, but not limited to, those described in commonly ownedU.S. patent application Ser. No. 15/840,146, filed on Dec. 13, 2017,which is hereby incorporated by reference.

The final ceramic structure, even when no machining, polishing, bonding,surface finishing, or assembly is required, may be subjected to coloring(e.g., with inks or dyes), stamping, or other non-functional features,if desired.

In this detailed description, reference has been made to multipleembodiments and to the accompanying drawings in which are shown by wayof illustration specific exemplary embodiments of the invention. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatmodifications to the various disclosed embodiments may be made by askilled artisan.

Where methods and steps described above indicate certain eventsoccurring in certain order, those of ordinary skill in the art willrecognize that the ordering of certain steps may be modified and thatsuch modifications are in accordance with the variations of theinvention. Additionally, certain steps may be performed concurrently ina parallel process when possible, as well as performed sequentially.

All publications, patents, and patent applications cited in thisspecification are herein incorporated by reference in their entirety asif each publication, patent, or patent application were specifically andindividually put forth herein.

This specification hereby incorporates by reference Eckel et al.,“Additive manufacturing of polymer-derived ceramics” Science, volume351, issue 6268, pages 58-62, January 2016.

The embodiments, variations, and figures described above should providean indication of the utility and versatility of the present invention.Other embodiments that do not provide all of the features and advantagesset forth herein may also be utilized, without departing from the spiritand scope of the present invention. Such modifications and variationsare considered to be within the scope of the invention defined by theclaims.

What is claimed is:
 1. A preceramic radiation-curable resin compositioncomprising a metal-containing hydrosilylation catalyst and a moleculehaving the formula:

wherein: x=1 to 100 when repeat units are connected linearly or x=1 to10 when repeat units are connected cyclically; y=0 to 100 when repeatunits are connected linearly or are not present, or y=0 to 10 whenrepeat units are connected cyclically or are not present; R₁ is selectedfrom the group consisting of hydrogen, a C₁-C₁₈ unsubstituted orsubstituted group, a halide, an ester group, an amine group, a hydroxylgroup, a cyano group, and combinations thereof; R₂ is selected from thegroup consisting of hydrogen, a C₁-C₁₈ unsubstituted or substitutedgroup, a halide, an ester group, an amine group, a hydroxyl group, acyano group, and combinations thereof; R₃ is selected from the groupconsisting of hydrogen, a C₁-C₁₈ unsubstituted or substituted group, ahalide, an ester group, an amine group, a hydroxyl group, a cyano group,and combinations thereof; R₄ is a UV-active functional group that iscapable of free-radical polymerization, cationic polymerization, or bothof these; and the carbon-carbon bond between R₄ and Si, depicted as

, is a single bond (C—C) or a double bond (C═C).
 2. The composition ofclaim 1, wherein R₄ is selected from the group consisting of acrylate,methacrylate, vinyl ether, epoxide, cycloaliphatic epoxide, oxetane,thiol, alkyne, and combinations, analogues, or derivatives thereof. 3.The composition of claim 2, wherein R₄ is a thiol, said compositionfurther comprising an additional molecule comprising two or moreunsaturated C═X double bonds, two or more C≡X triple bonds, or at leastone C═X double bond and at least one C≡X triple bond, wherein X isselected from C, S, O, N, or combinations thereof.
 4. The composition ofclaim 1, said composition further comprising a photoinitiator that iseffective to initiate polymerization at said UV-active functional group.5. The composition of claim 4, said composition further comprising aradiation-trigger free-radical initiator active at a second wavelengththat is substantially different from a first wavelength for which saidphotoinitiator is active.
 6. The composition of claim 1, saidcomposition further comprising a free-radical inhibitor.
 7. Thecomposition of claim 1, said composition further comprising a3D-printing resolution agent selected from the group consisting of UVabsorbers, fluorescent molecules, optical brighteners, and combinationsthereof.
 8. The composition of claim 1, said composition furthercomprising from about 0.1 vol % to about 70 vol % of solid-phasefillers.
 9. A preceramic resin precursor formulation comprising: (a) afirst material containing first molecules comprising at least one Si—Cbond, at least one Si—N bond, or at least one Si—C bond and at least oneSi—N bond, wherein at least one of said first molecules comprises asilyl hydride group (Si—H) available for hydrosilylation; (b) a secondmaterial containing second molecules with at least one unsaturatedcarbon-carbon double bond attached to an R₄ group (R₄—C═C), and/or atleast one carbon-carbon triple bond attached an R₄ group (R₄—C≡C),wherein R₄ is a UV-active functional group; and (c) a homogeneous orheterogeneous metal-containing catalyst.
 10. The formulation of claim 9,wherein said first molecules contain side groups selected from the groupconsisting of hydrogen, halides, substituted or unsubstituted cyclic oracyclic alkyl groups, aryl groups, hydrocarbon groups containing C═Xdouble bonds or C≡X triple bonds (X is C, S, O, and/or N), andcombinations thereof.
 11. The formulation of claim 9, wherein said firstmolecules further contain one or more atoms selected from the groupconsisting of B, Al, Ti, Zn, Zr, O, N, P, S, Ge, and combinationsthereof.
 12. The formulation of claim 9, wherein said first moleculeshave the formula:

wherein: n=1 to 100 when repeat units are connected linearly, or n=2 to10 when repeat units are connected cyclically; R₁ is selected from thegroup consisting of hydrogen, a C₁-C₁₈ unsubstituted or substitutedgroup, a halide, an ester group, an amine group, a hydroxyl group, acyano group, and combinations thereof; R₂ is selected from the groupconsisting of hydrogen, a C₁-C₁₈ unsubstituted or substituted group, ahalide, an ester group, an amine group, a hydroxyl group, a cyano group,and combinations thereof; and R₃ is selected from the group consistingof hydrogen, a C₁-C₁₈ unsubstituted or substituted group, a halide, anester group, an amine group, a hydroxyl group, a cyano group, andcombinations thereof, with the proviso that at least one R₃ group ishydrogen.
 13. The formulation of claim 9, wherein R₄ is selected fromthe group consisting of acrylate, methacrylate, vinyl ether, epoxide,cycloaliphatic epoxide, oxetane, thiol, and combinations, analogues, orderivatives thereof.
 14. The formulation of claim 9, said formulationfurther comprising an aprotic organic solvent in a concentration fromabout 1 wt % to about 99 wt % in said formulation.
 15. The formulationof claim 9, said formulation further comprising an inhibitor in aconcentration from about 0.001 wt % to about 10 wt % in saidformulation.
 16. A method of making a preceramic radiation-curable resincomposition, said method comprising: (a) obtaining a first materialcontaining first molecules comprising at least one Si—C bond, at leastone Si—N bond, or at least one Si—C bond and at least one Si—N bond,wherein at least one of said first molecules comprises a silyl hydridegroup (Si—H) available for hydrosilylation; (b) obtaining a secondmaterial containing second molecules with at least one unsaturatedcarbon-carbon double bond attached to an R₄ group (R₄—C═C), and/or atleast one carbon-carbon triple bond attached an R₄ group (R₄—C≡C),wherein R₄ is a UV-active functional group; and (c) reacting, viahydrosilylation in the presence of a homogeneous or heterogeneousmetal-containing catalyst, said first material with said secondmaterial, to generate a third material containing third moleculescomprising at least one Si—C bond, at least one Si—N bond, or at leastone Si—C bond and at least one Si—N bond, wherein said third moleculesfurther comprise a R₄—C—C—Si sequence and/or a R₄—C═C—Si sequence as ahydrosilylation reaction product.
 17. The method of claim 16, wherein instep (c), the molar ratio of said second molecules to said firstmolecules is selected from about 1 to about n, wherein n is the averagenumber of silyl hydride groups present in each of said first molecules.18. The method of claim 16, said method further comprising combiningsaid third material with a catalyst quencher to capture or poison saidmetal-containing catalyst.
 19. The method of claim 16, wherein saidfirst molecules have the formula:

and wherein said third molecules have the formula:

wherein: m=1 to 100 and is the number of said second molecules thatreact with each of said first molecules; n=1 to 100 when repeat unitsare connected linearly, or n=2 to 10 when repeat units are connectedcyclically; n−m is 0 or greater; R₁ is selected from the groupconsisting of hydrogen, a C₁-C₁₈ unsubstituted or substituted group, ahalide, an ester group, an amine group, a hydroxyl group, a cyano group,and combinations thereof; R₂ is selected from the group consisting ofhydrogen, a C₁-C₁₈ unsubstituted or substituted group, a halide, anester group, an amine group, a hydroxyl group, a cyano group, andcombinations thereof; R₃ is selected from the group consisting ofhydrogen, a C₁-C₁₈ unsubstituted or substituted group, a halide, anester group, an amine group, a hydroxyl group, a cyano group, andcombinations thereof; and the carbon-carbon bond between R₄ and Si,depicted as

, is a single bond (C—C) or a double bond (C═C).
 20. The method of claim16, said method further comprising 3D printing and thermally treatingsaid preceramic radiation-curable resin composition to generate aceramic material.